MEMS Theory and Features

Introduction
Deep technical expertise in MEMS (Micro-electro-mechanical systems) technology, analog CMOS circuit design and development, and cost-effective assembly and test. The combination of this expertise, all of which is in-house, is unique in the timing industry and is driving innovation at an exponentially faster rate than quartz. MEMS innovation and leadership is revolutionizing the timing industry.

Robust and Reliable MEMS Technology
Our MEMS technology has roots in Bosch and Stanford University. Since incorporation, We have developed several generations of cutting-edge kHz and MHz MEMS resonators that have the highest performance, lowest drift, smallest size and best reliability in the industry. We’ve also developed a comprehensive development and simulation platform that ensures first silicon success for all our MEMS resonators. Our MEMS resonators are not only shipped in every product we sell, other semiconductor companies have integrated our MEMS resonators inside their SOCs to offer unique, high-volume solutions that don’t require external clocks.

Innovative, High Performance Analog Circuit Design
We have a world-class analog engineering team that has delivered the highest performance and most flexible oscillators in the industry. Since our first product introduction in 2006, we’ve improved frequency stability performance 250 times (as measured by Figure of Merit), improved jitter performance 800 times, improved Allan deviation 30,000 times and improved power consumption 100 times, all while continuing to maintain our product flexibility and reliability.

Cost Effective Assembly, Test and Integration
In addition to MEMS and analog circuit expertise, We also have the ability to deliver large volumes with excellent quality and reliability. This ability comes from our assembly, test, and calibration expertise, allowing us to offer a fully integrated solution that is completely pin compatible with industry standard footprints. This pin-compatibility allows customers to adopt MEMS timing solutions quickly and with minimal risk.

Inside MEMS
MEMS constitute the new frontier in frequency control technology and are a valid alternative to frequency devices based onto quartz crystal blanks. Main advantages of MEMS, respect to crystal blanks based products, is the all-in-one integration of resonator and IC, which determines a very compact and highly reliable integrated solution. MEMS resonator is produced into a very small silicon resonator die that is fully vacuum-sealed in silicon, extremely stable and highly durable. Because this process uses state-of-the-art CMOS foundry tools and materials, MEMS are highly manufacturable with excellent yields, quality and reliability.
The resonator structure is first etched in a silicon on insulator (SOI) layer using a deep reactive ion etching (DRIE) process. After the resonators are etched, the wafer surfaces are planarized by filling the trenches with oxide. The oxide is patterned to form contact holes that allow electrical connection to the resonator. Thin silicon layers are grown on top of the oxide and vents are patterned to allow removal of the oxide that surrounds the resonator beams. Oxide is removed with hydrofluoric acid vapor to create freestanding resonator beams, allowing the resonators to vibrate.
Final encapsulation is essential to forming stable resonators. This process is the only demonstrated fabrication process that produces MEMS resonators with stability that meets or exceeds that of quartz crystals. Within high-temperature epitaxial reactors, the resonators and vacuum cavities are cleaned with hydrogen and chlorine gas. The resonators are sealed with a durable poly silicon cap that protects the resonator die and enable them to withstand very high pressure.
Electrical vias are formed to the resonators and electrodes by etching and filling trenches. Electrical interconnects are made with aluminum traces and bond pads. The process is completed with final deposition of silicon oxide and nitride scratch masks steps. The resulting wafers can be back-grounded to less than 100 um thick and packaged with industry standard IC packaging processes such as plastic molding, flip chip and chip stack.

Our silicon MEMS resonators are available in die form and can be cost-effectively embedded with other die inside a standard plastic semiconductor package. Integrating a MEMS resonator offers numerous benefits. By completely eliminating external timing circuits, systems designers will experience enhanced performance, reduced board space, reduced support costs and faster time to revenue.
• Integration enables a high precision clock (±5 PPM or ±25 PPM)
• Eliminates all external clocks to simplify system design and reduce board space
• Simplifies technical support. Reduces customer issues related to bad layout practices, incorrect decoupling/filtering, and selection
of un-matched / inappropriate crystal resonator / oscillator
• Compatible with any standard packaging technology
• Enables a standard supply chain: scalable, shorter lead times, reduced BOM

A MEMS oscillator combines a MEMS resonator die with a programmable oscillator IC. Both die are mounted together through a stacked-die or flip-chip process and co-packaged in industry-standard plastic packages or chip-scale packaging.

As shown in the block diagram, a MEMS resonator is connected to the MEMS-specific circuit blocks on the analog oscillator IC and is driven through electrostatic excitation. A MEMS bias generator is used to bias the electrostatic transducers that are built in the MEMS die. The resonator sustaining circuit brings the resonator into mechanical oscillation.
The output frequency is configured through use of a Fractional-N phase locked loop (PLL) located on the analog oscillator die. In most families, the output drivers enable configurable drive strength for best matching of transmission line impedances and to reduce system EMI. On-chip one time programmable (OTP) memory is used to store the configuration parameters.

Our MEMS technology reduces the need for temperature compensation. This simplifies the design of the analog oscillator IC, reduces system size and lowers power consumption. In some MEMS oscillator families, the functional blocks associated with temperature compensated can be eliminated (as shown in the diagram above). For precision timing applications (< ±25 PPM), ultra-performance XOs, differential XOs, VCXOs and TCXOs employ a temperature sensor and a temperature to digital converter (as shown in figure) which work with the Frac-N PLL to perform temperature compensation.

Dual MEMS
For a even higher temperature compensation process We have developed also a Dual MEMS architecture.
This architecture combines the world’s most accurate temperature sensor with a proprietary temperature compensation scheme and a low-noise frequency synthesizer. Together these elements deliver excellent dynamic performance, ultra-low jitter, wide frequency range, and programmability.
Underlying this architecture is an extremely accurate silicon temperature sensor. This temperature sensing scheme is based on two MEMS resonators fabricated on the same die, a unique construction only possible with silicon MEMS technology and not with quartz. One MEMS resonator is designed with flat frequency characteristic over temperature; the second resonator is sensitive to temperature changes and acts as a temperature sensor. The ratio of frequencies between these two resonators provides an accurate reading of the resonator temperature with 30 µK resolution.
DualMEMS design eliminates thermal gradients between the MEMS resonator and the MEMS temperature sensor. There is no lag between the resonator and sensor since both MEMS are located on the same die substrate as physically close to each other as possible, with only 100 µm separating the two elements. Additionally, the timing resonator and the temperature sensor resonator are thermally shunted through

silicon, which is an excellent conductor of heat. This design greatly reduces the time constant for heat transfer between the resonator and the temperature sensor. Silicon MEMS microfabrication enables both the resonator and the temperature sensor resonator to have an identical construction with the same (very small) mass and equivalent thermal paths to the environment so that the temperature of both MEMS are raised and lowered together, without lag.
Because the MEMS are nearly perfectly thermally coupled, temperature tracking is 40 times faster than quartz TCXOs, ensuring the best dynamic performance under airflow and rapid temperature changes.

The DualMEMS structure is paired with a mixed-signal CMOS IC with a state-of-the-art temperature compensation circuit, and together these elements provide high effective compensation. In addition to the low-noise PLL, the highly integrated CMOS IC contains on-chip regulators, a TDC (temperature to digital converter) and support for any frequency between 1 and 700 MHz.

Because the two MEMS are co-located on the same die (comprising the DualMEMS) and mounted directly on top of the temperature compensation and PLL circuitry in the CMOS die, there is tight coupling between all elements in the oscillator. This compensation design, with compensation bandwidth that runs at 100s of Hz, achieves the best dynamic performance that is maintained under rapidly changing environmental conditions. Compensation for temperature transients much faster than any quartz-based TCXO.
In contrast to DualMEMS solution, quartz TCXO performance is fundamentally hindered by the use of a discrete temperature sensor (e.g. a BJT bandgap temperature sensor or a thermistor) and compensation circuitry that is located on the oscillator IC at a distance from the resonator. In quartz TCXOs, the crystal resonator is mounted on pads and connected to the oscillator IC through vias. A separation between the resonator and oscillator IC must be maintained so the crystal can freely vibrate. The lack of thermal coupling between the crystal resonator and a separate temperature sensor makes it impossible to design a faster temperature compensation loop without causing loop stability issues. As a result, quartz-based TCXOs typically have compensation bandwidth of 5 to 10 Hz, too slow to track rapid change, and causing abrupt frequency jumps when subjected to airflow and/or temperature perturbation.
Our MEMS timing solutions have a flexible architecture that is supported by factory programmability. This architecture allows customers to order a device configured to meet their exact design specifications, and receive samples within one week and production volume within three to five weeks. Designers have the option to use the Time Machine II programmer to instantly program oscillators in their own lab or office to optimize system performance and quickly develop prototypes.
With access to this wide range of specifications and features, customers can eliminate multiple suppliers and qualification efforts. The result is lower cost of ownership and a simplified supply chain.

Customizable frequency 1Hz to 625MHz with up 6 decimals of accuracy
Frequency stability ±1.5, ±2.5, ±3, ±5, ±10, ±20, ±25 or ±50 PPM
Temperature range 0 to +70°C, -10 to +70°C, -20 to +70°C, -40 to +85°C, -40 to +105°C, -40 to +125°C or -55 to +125°C
Supply Voltage MHz LVCMOS devices: 1.8, 2.5 to 3.3V
Differential devices: 2.5 to 3.3V
kHz devices: 1.2 to 3.63V
Output signaling type Single-ended devices: LVCMOS LVTTL or NanoDrive
Differential devices: LVPECL, LVDS, HCSL or CML
Industry standard Packages 2012, 2016, 2520, 5032 or 7050 SMD packages for drop-in replacement of quartz
3225 SMD – World’s thinnest oscillator package at 0.25 mm height
Special packages 1508 chip-scale package – World’s smallest oscillator package
SOT23-5 – For highest board-level reliability
Special functions Spread spectrum (down and center spread) and digital control (DCXO)
Pull range Programmable from ±25 to ±1600 PPM with 1% linearity
(Available in VCMO, VCTCMO and DCMO lines)
Drive strength Programmable high and low drive strength settings for best EMI or driving multiple loads
Control Input Output enable, spread disable, standby or no connect

Programmable Frequency
Our oscillators offer any frequency within the operating range with up to 6 decimal places of accuracy. With custom frequencies, designers can increase system performance (microprocessor / FPGA applications) and reduce bit error rates (Ethernet applications). Samples and low-volume orders are customized and delivered within 1 week; production quantities are available in 3-5 weeks for most oscillator families.

Frequency Stability
MEMS timing devices offer a range of frequency stability options. For applications that require ultra-stable frequency, We offer ±1.5 PPM stability in TCXO and VCTCXO families that operate over the full industrial temperature range. Within each product category (kHz, XO, VCXO, VCTCXO, etc.), a variety of frequency stability options are available to best meet the application requirement with the lowest cost.

Temperature Range
Our MEMS products are available in a variety of operating temperature ranges. These wide temperature ranges, combined with inherently robust and highly reliable design, ensures that devices are well suited for the application environment and available at the lowest cost. High temperature families provide the widest combination of frequencies, stability and small package size – a combination not available from quartz suppliers.

Supply Voltage
Covering the most common input-output voltages used, MHz products can operate at 1.8 volts and at any voltage between 2.5 and 3.3 volts. KHz products, which are optimized for battery-powered applications, operate between 1.2 and 3.63 volts. All of these voltage levels are available across the entire frequency range, a feature that quartz-based solutions cant offer. Because our products are configured to operate at the required voltage, external components such as level translators or additional regulators are not required, reducing board space and cost.

Spread Spectrum
Our MEMS offers spread-spectrum capability with center-spread and down-spread options, as well as different values of spreading. This feature provides an excellent solution for easily solving EMI problems which are often detected at the last stage of product development. At this late stage, the only options available may be to redesign / relayout the board or to add shielding within the case, both of which are expensive. Spread-spectrum devices, which are pin-compatible with quartz oscillators, can solve EMI problems without system redesign or expensive shielding.

Digital Control
Digitally-controlled oscillators (DCXOs) are ideal for jitter cleaning and fail-safe functions in high-speed applications. The features of these devices are controlled by programming appropriate values serially, in-system by using a single-pin (1-wire interface). DCXOs eliminate the need for an external digital-to-analog converter (DAC) in the control path. This reduces board complexity and improves performance, as system noise is much lower.

Pull Range
VCXOs, VCTCXOs and DCXOs offer the widest pull range (as much as ±25 to ±1600 PPM) with the industry’s best linearity at 1%. The superior tuning slope (Kv) consistency and linearity of our oscillators enable a host of benefits including simpler loop control in software controlled PLLs, faster calibration and lock time, more consistent PLL bandwidth over operating range, reduced modulation harmonics, tighter PLL bandwidth design and more robust system performance. Compared to quartz devices with pull range limited to ±200 PPM and linearity at 10%, our MEMS timing devices are 8 and 10 times better respectively.

Programmable Drive Strength Control
All of our MHz products have programmable drive strength control using SoftEdge technology. This feature allows designers to accurately match the output impedance of the oscillator with the trace impedance of the board to reduce reflections. Higher drive strength can be selected to drive multiple loads and eliminate external buffers. Lower drive strength can be used to improve signal integrity and reduce EMI.

Field Programmable Prototyping
We offer the Time Machine II, a complete programming kit for use with field programmable timing devices. This kit allows system designers to quickly and easily program oscillators according to the specifications and configuration required. Using field programmable devices, available in a wide range of package sizes, operating temperatures and signally types, design-specific samples can be generated in less than a minute.
The specification that can be customized with the Time Machine II programmer include frequency (with 6 decimal places of accuracy), frequency stability, supply voltage, drive strength control, pull range (in VCXOs and DCXOs) and center/down spread (in SSXOs).
The frequency output of all oscillators, whether quartz- and MEMS-based, varies over temperature. This variation is a crucial performance specification that is expressed as frequency stability and measured in parts per million (PPM). This stability rating is inclusive of variation over temperature, voltage, process and soldering.

32 kHz XO Frequency Stability
In terms of frequency stability, our revolutionary MEMS 32 kHz oscillators are two times more accurate than quartz XTALs. The measured frequency variation of MEMS-based 32 kHz oscillators is plotted in blue lines as shown below. The red lines represent the frequency variation range of 32 kHz crystal resonators (XTALs). At room temperature (25°C), SiTime’s 32 kHz devices are trimmed to < 10 PPM, while quartz XTALs demonstrate 20 PPM variation. Over the entire industrial temperature range, our devices exhibit < 75 to 100 PPM stability compared to typical quartz XTALs with -160 to -200 PPM.

Introduction
Deep technical expertise in MEMS (Micro-electro-mechanical systems) technology, analog CMOS circuit design and development, and cost-effective assembly and test. The combination of this expertise, all of which is in-house, is unique in the timing industry and is driving innovation at an exponentially faster rate than quartz. MEMS innovation and leadership is revolutionizing the timing industry.

Robust and Reliable MEMS Technology
Our MEMS technology has roots in Bosch and Stanford University. Since incorporation, We have developed several generations of cutting-edge kHz and MHz MEMS resonators that have the highest performance, lowest drift, smallest size and best reliability in the industry. We’ve also developed a comprehensive development and simulation platform that ensures first silicon success for all our MEMS resonators. Our MEMS resonators are not only shipped in every product we sell, other semiconductor companies have integrated our MEMS resonators inside their SOCs to offer unique, high-volume solutions that don’t require external clocks.

Innovative, High Performance Analog Circuit Design
We have a world-class analog engineering team that has delivered the highest performance and most flexible oscillators in the industry. Since our first product introduction in 2006, we’ve improved frequency stability performance 250 times (as measured by Figure of Merit), improved jitter performance 800 times, improved Allan deviation 30,000 times and improved power consumption 100 times, all while continuing to maintain our product flexibility and reliability.

Cost Effective Assembly, Test and Integration
In addition to MEMS and analog circuit expertise, We also have the ability to deliver large volumes with excellent quality and reliability. This ability comes from our assembly, test, and calibration expertise, allowing us to offer a fully integrated solution that is completely pin compatible with industry standard footprints. This pin-compatibility allows customers to adopt MEMS timing solutions quickly and with minimal risk.

Inside MEMS
MEMS constitute the new frontier in frequency control technology and are a valid alternative to frequency devices based onto quartz crystal blanks. Main advantages of MEMS, respect to crystal blanks based products, is the all-in-one integration of resonator and IC, which determines a very compact and highly reliable integrated solution. MEMS resonator is produced into a very small silicon resonator die that is fully vacuum-sealed in silicon, extremely stable and highly durable. Because this process uses state-of-the-art CMOS foundry tools and materials, MEMS are highly manufacturable with excellent yields, quality and reliability.
The resonator structure is first etched in a silicon on insulator (SOI) layer using a deep reactive ion etching (DRIE) process. After the resonators are etched, the wafer surfaces are planarized by filling the trenches with oxide. The oxide is patterned to form contact holes that allow electrical connection to the resonator. Thin silicon layers are grown on top of the oxide and vents are patterned to allow removal of the oxide that surrounds the resonator beams. Oxide is removed with hydrofluoric acid vapor to create freestanding resonator beams, allowing the resonators to vibrate.
Final encapsulation is essential to forming stable resonators. This process is the only demonstrated fabrication process that produces MEMS resonators with stability that meets or exceeds that of quartz crystals. Within high-temperature epitaxial reactors, the resonators and vacuum cavities are cleaned with hydrogen and chlorine gas. The resonators are sealed with a durable poly silicon cap that protects the resonator die and enable them to withstand very high pressure.
Electrical vias are formed to the resonators and electrodes by etching and filling trenches. Electrical interconnects are made with aluminum traces and bond pads. The process is completed with final deposition of silicon oxide and nitride scratch masks steps. The resulting wafers can be back-grounded to less than 100 um thick and packaged with industry standard IC packaging processes such as plastic molding, flip chip and chip stack.

Our silicon MEMS resonators are available in die form and can be cost-effectively embedded with other die inside a standard plastic semiconductor package. Integrating a MEMS resonator offers numerous benefits. By completely eliminating external timing circuits, systems designers will experience enhanced performance, reduced board space, reduced support costs and faster time to revenue.
• Integration enables a high precision clock (±5 PPM or ±25 PPM)
• Eliminates all external clocks to simplify system design and reduce board space
• Simplifies technical support. Reduces customer issues related to bad layout practices, incorrect decoupling/filtering, and selection
of un-matched / inappropriate crystal resonator / oscillator
• Compatible with any standard packaging technology
• Enables a standard supply chain: scalable, shorter lead times, reduced BOM

A MEMS oscillator combines a MEMS resonator die with a programmable oscillator IC. Both die are mounted together through a stacked-die or flip-chip process and co-packaged in industry-standard plastic packages or chip-scale packaging.

As shown in the block diagram, a MEMS resonator is connected to the MEMS-specific circuit blocks on the analog oscillator IC and is driven through electrostatic excitation. A MEMS bias generator is used to bias the electrostatic transducers that are built in the MEMS die. The resonator sustaining circuit brings the resonator into mechanical oscillation.
The output frequency is configured through use of a Fractional-N phase locked loop (PLL) located on the analog oscillator die. In most families, the output drivers enable configurable drive strength for best matching of transmission line impedances and to reduce system EMI. On-chip one time programmable (OTP) memory is used to store the configuration parameters.

Our MEMS technology reduces the need for temperature compensation. This simplifies the design of the analog oscillator IC, reduces system size and lowers power consumption. In some MEMS oscillator families, the functional blocks associated with temperature compensated can be eliminated (as shown in the diagram above). For precision timing applications (< ±25 PPM), ultra-performance XOs, differential XOs, VCXOs and TCXOs employ a temperature sensor and a temperature to digital converter (as shown in figure) which work with the Frac-N PLL to perform temperature compensation.

Dual MEMS
For a even higher temperature compensation process We have developed also a Dual MEMS architecture.
This architecture combines the world’s most accurate temperature sensor with a proprietary temperature compensation scheme and a low-noise frequency synthesizer. Together these elements deliver excellent dynamic performance, ultra-low jitter, wide frequency range, and programmability.
Underlying this architecture is an extremely accurate silicon temperature sensor. This temperature sensing scheme is based on two MEMS resonators fabricated on the same die, a unique construction only possible with silicon MEMS technology and not with quartz. One MEMS resonator is designed with flat frequency characteristic over temperature; the second resonator is sensitive to temperature changes and acts as a temperature sensor. The ratio of frequencies between these two resonators provides an accurate reading of the resonator temperature with 30 µK resolution.
DualMEMS design eliminates thermal gradients between the MEMS resonator and the MEMS temperature sensor. There is no lag between the resonator and sensor since both MEMS are located on the same die substrate as physically close to each other as possible, with only 100 µm separating the two elements. Additionally, the timing resonator and the temperature sensor resonator are thermally shunted through

silicon, which is an excellent conductor of heat. This design greatly reduces the time constant for heat transfer between the resonator and the temperature sensor. Silicon MEMS microfabrication enables both the resonator and the temperature sensor resonator to have an identical construction with the same (very small) mass and equivalent thermal paths to the environment so that the temperature of both MEMS are raised and lowered together, without lag.
Because the MEMS are nearly perfectly thermally coupled, temperature tracking is 40 times faster than quartz TCXOs, ensuring the best dynamic performance under airflow and rapid temperature changes.

The DualMEMS structure is paired with a mixed-signal CMOS IC with a state-of-the-art temperature compensation circuit, and together these elements provide high effective compensation. In addition to the low-noise PLL, the highly integrated CMOS IC contains on-chip regulators, a TDC (temperature to digital converter) and support for any frequency between 1 and 700 MHz.

Because the two MEMS are co-located on the same die (comprising the DualMEMS) and mounted directly on top of the temperature compensation and PLL circuitry in the CMOS die, there is tight coupling between all elements in the oscillator. This compensation design, with compensation bandwidth that runs at 100s of Hz, achieves the best dynamic performance that is maintained under rapidly changing environmental conditions. Compensation for temperature transients much faster than any quartz-based TCXO.
In contrast to DualMEMS solution, quartz TCXO performance is fundamentally hindered by the use of a discrete temperature sensor (e.g. a BJT bandgap temperature sensor or a thermistor) and compensation circuitry that is located on the oscillator IC at a distance from the resonator. In quartz TCXOs, the crystal resonator is mounted on pads and connected to the oscillator IC through vias. A separation between the resonator and oscillator IC must be maintained so the crystal can freely vibrate. The lack of thermal coupling between the crystal resonator and a separate temperature sensor makes it impossible to design a faster temperature compensation loop without causing loop stability issues. As a result, quartz-based TCXOs typically have compensation bandwidth of 5 to 10 Hz, too slow to track rapid change, and causing abrupt frequency jumps when subjected to airflow and/or temperature perturbation.
Our MEMS timing solutions have a flexible architecture that is supported by factory programmability. This architecture allows customers to order a device configured to meet their exact design specifications, and receive samples within one week and production volume within three to five weeks. Designers have the option to use the Time Machine II programmer to instantly program oscillators in their own lab or office to optimize system performance and quickly develop prototypes.
With access to this wide range of specifications and features, customers can eliminate multiple suppliers and qualification efforts. The result is lower cost of ownership and a simplified supply chain.

Customizable frequency 1Hz to 625MHz with up 6 decimals of accuracy
Frequency stability ±1.5, ±2.5, ±3, ±5, ±10, ±20, ±25 or ±50 PPM
Temperature range 0 to +70°C, -10 to +70°C, -20 to +70°C, -40 to +85°C, -40 to +105°C, -40 to +125°C or -55 to +125°C
Supply Voltage MHz LVCMOS devices: 1.8, 2.5 to 3.3V
Differential devices: 2.5 to 3.3V
kHz devices: 1.2 to 3.63V
Output signaling type Single-ended devices: LVCMOS LVTTL or NanoDrive
Differential devices: LVPECL, LVDS, HCSL or CML
Industry standard Packages 2012, 2016, 2520, 5032 or 7050 SMD packages for drop-in replacement of quartz
3225 SMD – World’s thinnest oscillator package at 0.25 mm height
Special packages 1508 chip-scale package – World’s smallest oscillator package
SOT23-5 – For highest board-level reliability
Special functions Spread spectrum (down and center spread) and digital control (DCXO)
Pull range Programmable from ±25 to ±1600 PPM with 1% linearity
(Available in VCMO, VCTCMO and DCMO lines)
Drive strength Programmable high and low drive strength settings for best EMI or driving multiple loads
Control Input Output enable, spread disable, standby or no connect

Programmable Frequency
Our oscillators offer any frequency within the operating range with up to 6 decimal places of accuracy. With custom frequencies, designers can increase system performance (microprocessor / FPGA applications) and reduce bit error rates (Ethernet applications). Samples and low-volume orders are customized and delivered within 1 week; production quantities are available in 3-5 weeks for most oscillator families.

Frequency Stability
MEMS timing devices offer a range of frequency stability options. For applications that require ultra-stable frequency, We offer ±1.5 PPM stability in TCXO and VCTCXO families that operate over the full industrial temperature range. Within each product category (kHz, XO, VCXO, VCTCXO, etc.), a variety of frequency stability options are available to best meet the application requirement with the lowest cost.

Temperature Range
Our MEMS products are available in a variety of operating temperature ranges. These wide temperature ranges, combined with inherently robust and highly reliable design, ensures that devices are well suited for the application environment and available at the lowest cost. High temperature families provide the widest combination of frequencies, stability and small package size – a combination not available from quartz suppliers.

Supply Voltage
Covering the most common input-output voltages used, MHz products can operate at 1.8 volts and at any voltage between 2.5 and 3.3 volts. KHz products, which are optimized for battery-powered applications, operate between 1.2 and 3.63 volts. All of these voltage levels are available across the entire frequency range, a feature that quartz-based solutions cant offer. Because our products are configured to operate at the required voltage, external components such as level translators or additional regulators are not required, reducing board space and cost.

Spread Spectrum
Our MEMS offers spread-spectrum capability with center-spread and down-spread options, as well as different values of spreading. This feature provides an excellent solution for easily solving EMI problems which are often detected at the last stage of product development. At this late stage, the only options available may be to redesign / relayout the board or to add shielding within the case, both of which are expensive. Spread-spectrum devices, which are pin-compatible with quartz oscillators, can solve EMI problems without system redesign or expensive shielding.

Digital Control
Digitally-controlled oscillators (DCXOs) are ideal for jitter cleaning and fail-safe functions in high-speed applications. The features of these devices are controlled by programming appropriate values serially, in-system by using a single-pin (1-wire interface). DCXOs eliminate the need for an external digital-to-analog converter (DAC) in the control path. This reduces board complexity and improves performance, as system noise is much lower.

Pull Range
VCXOs, VCTCXOs and DCXOs offer the widest pull range (as much as ±25 to ±1600 PPM) with the industry’s best linearity at 1%. The superior tuning slope (Kv) consistency and linearity of our oscillators enable a host of benefits including simpler loop control in software controlled PLLs, faster calibration and lock time, more consistent PLL bandwidth over operating range, reduced modulation harmonics, tighter PLL bandwidth design and more robust system performance. Compared to quartz devices with pull range limited to ±200 PPM and linearity at 10%, our MEMS timing devices are 8 and 10 times better respectively.

Programmable Drive Strength Control
All of our MHz products have programmable drive strength control using SoftEdge technology. This feature allows designers to accurately match the output impedance of the oscillator with the trace impedance of the board to reduce reflections. Higher drive strength can be selected to drive multiple loads and eliminate external buffers. Lower drive strength can be used to improve signal integrity and reduce EMI.

Field Programmable Prototyping
We offer the Time Machine II, a complete programming kit for use with field programmable timing devices. This kit allows system designers to quickly and easily program oscillators according to the specifications and configuration required. Using field programmable devices, available in a wide range of package sizes, operating temperatures and signally types, design-specific samples can be generated in less than a minute.
The specification that can be customized with the Time Machine II programmer include frequency (with 6 decimal places of accuracy), frequency stability, supply voltage, drive strength control, pull range (in VCXOs and DCXOs) and center/down spread (in SSXOs).
The frequency output of all oscillators, whether quartz- and MEMS-based, varies over temperature. This variation is a crucial performance specification that is expressed as frequency stability and measured in parts per million (PPM). This stability rating is inclusive of variation over temperature, voltage, process and soldering.

32 kHz XO Frequency Stability
In terms of frequency stability, our revolutionary MEMS 32 kHz oscillators are two times more accurate than quartz XTALs. The measured frequency variation of MEMS-based 32 kHz oscillators is plotted in blue lines as shown below. The red lines represent the frequency variation range of 32 kHz crystal resonators (XTALs). At room temperature (25°C), SiTime’s 32 kHz devices are trimmed to < 10 PPM, while quartz XTALs demonstrate 20 PPM variation. Over the entire industrial temperature range, our devices exhibit < 75 to 100 PPM stability compared to typical quartz XTALs with -160 to -200 PPM.

mems theory 04

With temperature compensation added, 32 kHz TCXOs exhibit frequency stability well within their ±5 PPM specification over temperature as shown below. We have achieved TCXO-level stability in a timing solution that consumes up to 50% less power and is up to 80% smaller than quartz-based solutions.


MEMS MHz Oscillator Frequency Stability
The frequency variation of standard AT cut quartz crystal oscillators is shown below, along with the stability of our typical MEMS oscillators. Since our revolutionary MEMS oscillators have built-in temperature compensation, these devices exhibit very flat frequency stability over the entire industrial temperature range, with adequate margin at the low and high temperatures to meet the specifications of high performance applications.
We offer a 10 PPM MO, as shown in the plot below, which quartz companies cannot offer. In fact, our 10-25 PPM MOs outperform quartz, SAW, and overtone oscillators at frequencies above 70 MHz. This is another fundamental change that We are bringing to the timing market.


We also offer 25 PPM MOs, as shown in the plot below, that have better frequency stability characteristics compared to quartz 25 PPM MOs.

Phase noise
Phase noise, and its time domain counterpart jitter, is one of the most important specifications of an oscillator. Phase noise and jitter have a direct impact on system performance, affecting such parameters as bit error ratio (BER) in serial data systems. Wireless and GPS applications have stringent requirements for close-in phase noise (< 10 kHz offset) while serial communications applications such as SONET, 10 Gigabit Ethernet, SyncE, SATA, SAS, Fibre Channel, and PCI-Express have specifications for RMS phase jitter (integrated over 12 kHz to 20 MHz offsets of the carrier frequency).

The phase noise and phase jitter of our MEMS oscillators have seen a dramatic improvement over the past 10 years. We use a highly optimized voltage controlled oscillator (VCO) along with a low noise, high-resolution TDC to achieve excellent phase noise performance. The phase noise plot below shows measured data of a TCXO with integrated phase jitter (IPJ) of only 82 femtoseconds (fs) RMS using the IEEE802.3-2015 10 GbE jitter tolerance mask of 1.875 to 20 MHz.
In root sum square (RSS) terms, our TCMO reference clock consumes only 0.024% of the total system random jitter budget of 4.1 ps RMS.
TCXOs also easily meet 40 GbE (4 x 10 GbE) and 100 GbE (10 x 10 GbE) jitter requirements, contributing only 0.37% to the total jitter budget under nominal conditions.

Importantly, the performance of TCXOs is maintained in wireless and serial data systems that are exposed to common environmental stressors such as shock and vibration. The plot below shows MEMS phase noise of a MEMS Super-TCXO compared to a best-in-class quartz TCXO. The random vibration magnitude was 7.5g root mean square (rms) over a frequency band of 15 Hz to 2 KHz.

The MEMS TCXO demonstrates about 20 times lower phase noise in this vibration frequency band. This is a significant benefit to systems facing these kinds of stresses because vibration immunity improves performance and reliability in communications systems deployed near train stations, subway stations, airports and many other locations that experience vibration.
This vibration immunity is due in large part to the small mass of MEMS resonators which have approximately 1,000 to 3,000 times lower mass than quartz resonators. This means a given acceleration imposed on a MEMS structure, such as from shock or vibration, will result in much lower force than its quartz equivalent and therefore induce a much lower frequency shift.

Reliable and Robust
A comparison of MEMS oscillator and quartz oscillator reliability and robustness is shown below.

  MEMS Oscillators Quartz Oscillators
Reliability / MTBF 1000 million hours 14-38 million hours
Shock Resistance 50,000 g shock 5,000 g shock
Vibration Resistance 70 g vibration 10 g vibration

Silicon-level Quality
MEMS-based devices leverage a combination of high quality materials, sophisticated processes and well-established infrastructure. Purified monocrystalline silicon, the base material used for semiconductors and MEMS die, is fundamentally a pure, strong and stable material. MEMS resonators are etched in silicon wafers and encapsulated under a layer of poly-silicon that makes them extremely robust. MEMS resonator wafers are made in CMOS facilities using batch-manufacturing to produce devices with predictability and nanometer precision. Six Sigma philosophy for process design and process control in combination with proven design rules ensures high quality. Learn more about how MEMS are manufactured.

Product Resilience
We have leveraged the inherent advantages of silicon, and developed the most reliable and robust timing solutions with a proprietary resonator structure and manufacturing process. Our MEMS resonators are vacuum-sealed using an advanced process that eliminates foreign particles and improves reliability. The very small mass and design of our resonators make them extremely immune to external forces. Using a single-point, center-anchored MEMS resonator that operates like a stiff spring, Our devices are designed to eliminate stress error sources. This resonator structure plus the oscillator IC design make the devices extremely immune to electromagnetic or power supply noise.
A key disadvantage of crystal oscillators is their susceptibility to vibration and the loss of stability with age. Vibration appears in the jitter performance of quartz devices. Silicon MEMS devices however, are not sensitive to vibration. MEMS devices resonate at a fundamental frequency in a mode that incident vibration does not modulate. Our oscillators have been tested along with comparable quartz oscillators to measure the effects of vibration, shock and electromagnetic noise.

Qualification and Testing
Our Quality Management System (QMS) is based on the ISO 9001:2016 quality system standard and all our products are designed and brought into production using our robust Six Sigma processes.
To ensure the highest quality, We perform Lot Acceptance Testing (LAT) over the temperature range on a sample of parts from each production lot. Our MEMS oscillators pass all standard CMOS qualifications and additional resonator-specific tests (listed below).
Test Description
EFR Early Life (125ºC 168 hrs dynamic)
HTOL High Temperature Operating Life (125ºC 2000 hrs dynamic)
ESD Electrostatic Discharge (HBM, MM, CDM)
LU Latch Up (85ºC 150 mA)
HAST Biased Temp and Humidity (85 hrs 130ºC 85% RH dynamic)
TC Temp Cycle (MSL1 + 1000 cycles, -65ºC -150ºC)
QA Quartz Style Aging (30 days 85ºC dynamic)
MS Mechanical Shock (50kg shock multi-axis dynamic)
VFV Variable Frequency Vibration (70g dynamic)
VF Vibration Fatigue (20g 30 hrs dynamic)
CA Constant Acceleration (30 kg dynamic)
HTS High Temperature Storage (125ºC 1000 hrs)
PCT Pressure Cooker Test (autoclave 120ºC 100% RH 2atm 96 hrs)
TS Temp Shock (-55ºC -125ºC 100 cycles)
MSL1 Moisture Sensitivity Level 1 (JEDEC)

With temperature compensation added, 32 kHz TCXOs exhibit frequency stability well within their ±5 PPM specification over temperature as shown below. We have achieved TCXO-level stability in a timing solution that consumes up to 50% less power and is up to 80% smaller than quartz-based solutions.

MEMS MHz Oscillator Frequency Stability
The frequency variation of standard AT cut quartz crystal oscillators is shown below, along with the stability of our typical MEMS oscillators. Since our revolutionary MEMS oscillators have built-in temperature compensation, these devices exhibit very flat frequency stability over the entire industrial temperature range, with adequate margin at the low and high temperatures to meet the specifications of high performance applications.
We offer a 10 PPM MO, as shown in the plot below, which quartz companies cannot offer. In fact, our 10-25 PPM MOs outperform quartz, SAW, and overtone oscillators at frequencies above 70 MHz. This is another fundamental change that We are bringing to the timing market.

We also offer 25 PPM MOs, as shown in the plot below, that have better frequency stability characteristics compared to quartz 25 PPM MOs.

Phase noise
Phase noise, and its time domain counterpart jitter, is one of the most important specifications of an oscillator. Phase noise and jitter have a direct impact on system performance, affecting such parameters as bit error ratio (BER) in serial data systems. Wireless and GPS applications have stringent requirements for close-in phase noise (< 10 kHz offset) while serial communications applications such as SONET, 10 Gigabit Ethernet, SyncE, SATA, SAS, Fibre Channel, and PCI-Express have specifications for RMS phase jitter (integrated over 12 kHz to 20 MHz offsets of the carrier frequency).

The phase noise and phase jitter of our MEMS oscillators have seen a dramatic improvement over the past 10 years. We use a highly optimized voltage controlled oscillator (VCO) along with a low noise, high-resolution TDC to achieve excellent phase noise performance. The phase noise plot below shows measured data of a TCXO with integrated phase jitter (IPJ) of only 82 femtoseconds (fs) RMS using the IEEE802.3-2015 10 GbE jitter tolerance mask of 1.875 to 20 MHz.
In root sum square (RSS) terms, our TCMO reference clock consumes only 0.024% of the total system random jitter budget of 4.1 ps RMS.
TCXOs also easily meet 40 GbE (4 x 10 GbE) and 100 GbE (10 x 10 GbE) jitter requirements, contributing only 0.37% to the total jitter budget under nominal conditions.

Importantly, the performance of TCXOs is maintained in wireless and serial data systems that are exposed to common environmental stressors such as shock and vibration. The plot below shows MEMS phase noise of a MEMS Super-TCXO compared to a best-in-class quartz TCXO. The random vibration magnitude was 7.5g root mean square (rms) over a frequency band of 15 Hz to 2 KHz.

The MEMS TCXO demonstrates about 20 times lower phase noise in this vibration frequency band. This is a significant benefit to systems facing these kinds of stresses because vibration immunity improves performance and reliability in communications systems deployed near train stations, subway stations, airports and many other locations that experience vibration.
This vibration immunity is due in large part to the small mass of MEMS resonators which have approximately 1,000 to 3,000 times lower mass than quartz resonators. This means a given acceleration imposed on a MEMS structure, such as from shock or vibration, will result in much lower force than its quartz equivalent and therefore induce a much lower frequency shift.

Reliable and Robust
A comparison of MEMS oscillator and quartz oscillator reliability and robustness is shown below.

  MEMS Oscillators Quartz Oscillators
Reliability / MTBF 1000 million hours 14-38 million hours
Shock Resistance 50,000 g shock 5,000 g shock
Vibration Resistance 70 g vibration 10 g vibration

Silicon-level Quality
MEMS-based devices leverage a combination of high quality materials, sophisticated processes and well-established infrastructure. Purified monocrystalline silicon, the base material used for semiconductors and MEMS die, is fundamentally a pure, strong and stable material. MEMS resonators are etched in silicon wafers and encapsulated under a layer of poly-silicon that makes them extremely robust. MEMS resonator wafers are made in CMOS facilities using batch-manufacturing to produce devices with predictability and nanometer precision. Six Sigma philosophy for process design and process control in combination with proven design rules ensures high quality. Learn more about how MEMS are manufactured.

Product Resilience
We have leveraged the inherent advantages of silicon, and developed the most reliable and robust timing solutions with a proprietary resonator structure and manufacturing process. Our MEMS resonators are vacuum-sealed using an advanced process that eliminates foreign particles and improves reliability. The very small mass and design of our resonators make them extremely immune to external forces. Using a single-point, center-anchored MEMS resonator that operates like a stiff spring, Our devices are designed to eliminate stress error sources. This resonator structure plus the oscillator IC design make the devices extremely immune to electromagnetic or power supply noise.
A key disadvantage of crystal oscillators is their susceptibility to vibration and the loss of stability with age. Vibration appears in the jitter performance of quartz devices. Silicon MEMS devices however, are not sensitive to vibration. MEMS devices resonate at a fundamental frequency in a mode that incident vibration does not modulate. Our oscillators have been tested along with comparable quartz oscillators to measure the effects of vibration, shock and electromagnetic noise.

Qualification and Testing
Our Quality Management System (QMS) is based on the ISO 9001:2016 quality system standard and all our products are designed and brought into production using our robust Six Sigma processes.
To ensure the highest quality, We perform Lot Acceptance Testing (LAT) over the temperature range on a sample of parts from each production lot. Our MEMS oscillators pass all standard CMOS qualifications and additional resonator-specific tests (listed below).
Test Description
EFR Early Life (125ºC 168 hrs dynamic)
HTOL High Temperature Operating Life (125ºC 2000 hrs dynamic)
ESD Electrostatic Discharge (HBM, MM, CDM)
LU Latch Up (85ºC 150 mA)
HAST Biased Temp and Humidity (85 hrs 130ºC 85% RH dynamic)
TC Temp Cycle (MSL1 + 1000 cycles, -65ºC -150ºC)
QA Quartz Style Aging (30 days 85ºC dynamic)
MS Mechanical Shock (50kg shock multi-axis dynamic)
VFV Variable Frequency Vibration (70g dynamic)
VF Vibration Fatigue (20g 30 hrs dynamic)
CA Constant Acceleration (30 kg dynamic)
HTS High Temperature Storage (125ºC 1000 hrs)
PCT Pressure Cooker Test (autoclave 120ºC 100% RH 2atm 96 hrs)
TS Temp Shock (-55ºC -125ºC 100 cycles)
MSL1 Moisture Sensitivity Level 1 (JEDEC)