September 20, 2021 Siliconizing the Timing Components Supply Chain

The semiconductor industry offers a robust, flexible and stable ecosystem for MEMS-based timing devices to serve the electronics industry.

Semiconductors are everywhere. In the past half-century, the semiconductor industry has grown into a global powerhouse and exceeds $400 billion annually. Along the way, semiconductors have transformed industries — photography film, magnetic storage, incandescent lighting and mechanical sensors — because they offer dramatic new functionality. Think about how you share photos or how you control home lighting today versus two decades ago. Even at the device level, semiconductors bring enhanced functionality and performance while simultaneously reducing power, size and design complexity. All these factors have led to the industry’s broad success. 

There is an arm of the semiconductor industry, microelectromechanical systems (MEMS), which are siliconizing sensing components such as gyroscopes, accelerometers and pressure sensors. The MEMS industry has been instrumental in bringing such specialized technology to the masses. Previously, gyroscopes were used only in specific technical equipment, such as navigation systems and virtual horizon displays in aircraft. Today, a smartphone includes a gyroscope and MEMS inertial sensors such as accelerometers. These enable dramatic new functionality, such as new functions for gaming, video stabilization, navigation and enhanced in-out features.

MEMS is now siliconizing another essential component in all electronics — timing.

So what do we mean by timing?

Timing is the heartbeat of electronic systems, delivering an accurate, stable and regular signal — like a human heartbeat — and providing a reference for all digital components in the system. Like a human heart, five timing parameters are important — absolute frequency, accuracy, stability, low noise and long-term performance.

Timing devices consist of passive resonators, active oscillators and integrated clock generators and buffers, each of which performs different functions. There are two essential components inside a timing device: a resonator that vibrates at a resonant frequency and an analog integrated circuit (IC) that converts these vibrations into electrical signals and distributes them. The resonator and IC are combined in a system-in-package (SIP) to form a complete solution.

In the past, most resonators have been quartz crystal-based. They exhibit piezoelectric effects and require a precise thickness and angular cut during manufacturing to achieve the required resonant frequency and stability over temperature, respectively. While quartz is a mature technology that has served the electronics industry for 70 years, it now has limitations such as fragility, susceptibility to mechanical stresses, rapid temperature changes, large size and aging effects.

Silicon MEMS technology has recently emerged as a superior alternative to quartz and has these advantages:

• Higher performance.
• Lower power.
• Smaller size.
• Superior flexibility through programmability.
• Higher reliability: better stability over time and temperature.
• More able to withstand the effects of temperature extremes, shock and vibration.

Supply Chain Resilience: MEMS Outperforms Quartz

Quartz and MEMS timing supply chains are fundamentally different and separate.

Quartz resonators require precision machining, which requires dedicated factories. To ramp up quartz manufacturing and packaging, quartz suppliers must build new factories at great expense. Conversely, MEMS resonators are manufactured on silicon wafers in semiconductor foundries, where the volume can be easily scaled up to meet higher demand.

Quartz has unique packaging characteristics. Quartz crystals must be packaged in a vacuum inside hermetically-sealed ceramic packages to enable accurate and reliable operation. There are few ceramic package suppliers globally, and according to various industry reports, a leading Japanese provider commands a 70% market share. Any disruption can impact the entire timing industry — as has happened before.

On the other hand, silicon MEMS resonators are dramatically smaller than quartz and operate in a die-level vacuum, eliminating the need for hermetically-sealed packages. MEMS-based timing devices can use various plastic packages and wafer-level chip-scale packaging (WLCSP). These packages are easy to manufacture and provided by all major semiconductor assembly providers (e.g., ASE, UTAC, Carsem).

The analog ICs for quartz oscillators usually get outsourced for development and manufacturing. And in many cases, they are manufactured in dedicated fabs associated with the quartz industry, which can be a problem. For example, in October 2020, a fire at a plant operated by Asahi Kasei Microdevices (AKM), a Japanese analog IC supplier, impacted many quartz timing suppliers. The resulting shortages had a cascading effect on many electronics markets, which are still being felt. Another example was the Great East Japan Earthquake of March 2011, which had a devastating impact on human life, communities, and industries. Many quartz factories in the region went offline for months, causing disruptions that reverberated throughout the industry. 

The analog ICs for MEMS are typically designed by the same companies that develop the MEMS resonators and are manufactured in large foundries such as TSMC. Given the tremendous capacity of global semiconductor foundries, scaling up silicon supplies is usually simply a matter of timely forecasting.

Despite recent shortages, semiconductor supply chains are still more flexible and responsive than quartz and can scale up or down to meet electronics’ demands. Industry watchers expect that the current semiconductor shortages will ease as the supply chain scales rapidly to meet forecasted demand.

Business continuity plans (BCP) require a diversity of supply, and having two independent sources is a tremendous advantage. In the timing industry, having two quartz suppliers is just not good enough, as each source may still use the same package or IC supplier. Instead, electronics companies must consider adding a completely disparate technology and supply chain, such as MEMS timing, to fulfill their BCP requirements. The added benefit of MEMS timing is that it also offers a performance advantage over quartz.

Compared to the inflexible, vendor-constrained quartz supply chain, the $440 billion global semiconductor industry provides a robust, flexible and stable ecosystem for MEMS-based timing devices to serve the needs of the ever-growing electronics industry. The siliconization of the timing industry has already begun. Whether for risk mitigation, inventory diversification, or a clear design advantage, learning about the benefits of MEMS timing is a sound first step to take.

www.sitime.com

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