MEMS-Based Timing Solutions Increase Reliability and Safety In Automotive Electronics

Around-the-Clock Automotive Safety and Reliability

From IoT devices to communications infrastructure to industrial and automotive systems, every electronic design relies on timing technology for accurate, stable frequency control of digital components. Timing devices range from passive resonators and active oscillators to integrated clock generators and buffers, each performing a different clocking function.

To keep automotive systems operating smoothly, a typical modern car uses more than 100 timing devices, and that number is growing as more cars adopt smarter technologies. Clocks and oscillators provide precise, reliable timing references for a wide array of automotive systems. They synchronize critical functions within electronic control units (ECUs) for advanced driver assistance systems (ADAS), in-vehicle networks, infotainment and other subsystems. Timing devices are also used to synchronize the transfer of huge amounts of data between dozens of sensors, ADAS computers, and rich, high-resolution displays. They enable Vehicle-to-Everything (V2X) and 5G communications in cars. Timing is also the foundation of global positioning system (GPS) technology and other global navigation satellite systems.

Automakers design cars to work reliably for many years while operating in harsh conditions. If an automotive component or system malfunctions, we still expect our cars to operate safely and reliably at all times. Timing devices must never be a weak link in automotive systems and continue to support safety-critical automotive functions. 

Automotive Is Gearing up with MEMS Timing

Traditionally, the most common clock source is a crystal oscillator, a 100-year-old technology that has matured to a point in which improvements are only marginal. Quartz crystals have fundamental limitations such as fragility and susceptibility to mechanical stresses. Automotive electronics operate in unforgiving environments subject to vibration, shock and temperature extremes, all of which can take a toll on sensitive quartz timing devices.

SiTime is disrupting the timing market by replacing fragile quartz devices with resonators based on microelectromechanical system (MEMS) technology. In fact, SiTime’s silicon MEMS resonators are 50 times more reliable than quartz, making them an ideal alternative to crystal oscillators in automotive designs.

Silicon MEMS technology is widely used in today’s electronics systems, from cell phones to automotive and aerospace applications. MEMS devices serve as gyroscopes, accelerometers (for instance, for airbag deployment), microphones, loudspeakers, sensors, magnetometers and many other functions. All silicon MEMS devices, including SiTime’s MEMS resonators, are manufactured at scale in mainstream fabs, providing proven, cost-effective technology for demanding applications.

MEMS Timing: A Perfect Fit for Automotive

MEMS-based timing components have proven to be advantageous in automotive applications, particularly for safety systems that enable automated driving including ADAS computers, gateways, cameras, and radar/lidar systems. Silicon MEMS technology is much more reliable than quartz crystals for clocking applications. This reliability is expressed in terms of failure per 10⁹ (billion) hours of operation or failure-in-time (FIT). Since 10⁹ hours is quite a long time to measure, the industry uses statistical analysis and accelerated models to determine FIT. The FIT rate of a silicon MEMS device is < 0.5 FIT (MTTF > 2 billion hours), calculated with 90% Confidence Level, which is 50x better than crystal technology.

Meeting Automotive Safety Integrity Levels

A low FIT rate is of prime value for automotive safety integrity level (ASIL) rated automotive systems. All ASIL-rated systems must go through functional safety certification based on the ISO 26262 standard. Part of this certification process consists of computing hardware safety metrics relative to a given target. For example, an ASIL D target is more difficult to meet than ASIL B. The FIT rate of individual elements in a system is used in this calculation. A better FIT rate for clock devices means better system-level safety metrics and greater ease in achieving higher ASIL ratings.

Advantages of Silicon Mems Timing

MEMS resonators are much smaller than quartz crystals, enabling smaller footprint timing devices (down to 1.0 mm x 1.2 mm) for space-sensitive automotive applications such as camera modules and radar/lidar sensors. Smaller size and less mass also mean more resilience to environmental shock and vibration.

Compared to quartz, MEMS resonators have 100x better resilience to electromagnetic interference (EMI) disturbances. This resiliency is especially beneficial for applications with high currents and electromagnetic fields, such as battery management systems for electric vehicles.

Silicon MEMS devices have excellent intrinsic material properties. For example, the frequency accuracy is very well controlled over a high-temperature range and does not diverge exponentially at extreme temperatures (a common crystal behavior). A typical MEMS oscillator has a stability of ±50 ppm over -40°C to +125°C, and some even achieve ±20 ppm – many multiples better than crystal oscillators. This number includes initial accuracy, temperature effects and aging. Adding temperature compensation increases stability up to ±0.1 ppm. This level of accuracy enables better synchronization of V2X and 5G communications over an extended temperature range.

In addition, MEMS timing is free from "cold start issues" at the bottom of the temperature range, which often plagues systems using quartz-based oscillators. Silicon MEMS resonators also are not subject to so-called "micro-jumps." These random, non-reproducible jumps in frequency, common with crystal oscillators, can result in a loss of signal for GNSS or V2X/5G communications. In fact, the frequency generated by a MEMS-based oscillator stays consistent even when the ambient temperature increases rapidly, while quartz-based oscillators output random frequencies with temperature spikes.

Automakers Require Dependable Timing Component Suppliers

SiTime is an established developer and manufacturer of innovative MEMS timing solutions with a strong track record as a dependable global supplier. SiTime’s supply chain is built for resilience. Silicon MEMS resonators are produced at a Bosch fab in Germany, while TSMC provides high-volume CMOS dies used in clock circuitry. Several assembly and test partners operate in parallel. SiTime also carries several months of MEMS and CMOS wafers, as well as finished goods, in inventory. All manufacturing partners have disaster recovery plans in place, which are reviewed and approved by SiTime. 

Timing components, as well as a reliable supply chain for these devices, are critical for today’s smart, connected automotive systems. For this reason, automakers and Tier 1 suppliers are making the shift from quartz technology to MEMS-based timing solutions, thereby enhancing the reliability of safety-critical automotive designs.

About the Author

Sumeet Kulkarni is the Director of Product Marketing, Automotive for SiTime. Prior to joining SiTime in August 2022, he held various director- and management-level positions at Texas Instruments and has 19 years of experience working in the semiconductor industry for automotive applications, encompassing integrated circuit design, marketing, and product management. Kulkarni earned a Bachelor of Engineering degree in electronics and telecommunications from the College of Engineering Pune, India, and a Master of Science degree from Technische Universität Darmstadt, Germany.