The MEMS Motion Sensor Perspectives

- Case Studies of the Technology and Business of MEMS Motion Sensors

A companion study guide for Foundations of MEMS textbook.

By Chang Liu

The MEMS technology and motion sensors market is growing rapidly. Motion sensors are fueling the growth of new consumer electronics devices, which in turn helps the growth of the MEMS industry. This article provides a review of the technology and business of MEMS motion sensors – accelerometer and gyroscopes. The article provides an inside view of the technology/business evolution and device at world’s major companies in this space – Analog Devices, MEMSIC, InvenSense, and STMicroelectronics. This document attempts to chronicle major development history of MEMS motion sensors up to 2010.

This article provides the following parts.

Part 1: Overview
Part 2: How it works
Part 3: Story of the pioneer – Analog Devices (1987-1993)
Part 4: Transition Era. MEMSIC’s innovation
Part 5: The InvenSense Story
Part 6: Sensor Fusion
Part 7: The STMicroelectronics Approach

Section 1: Overview - A History of MEMS Motion Sensors, Accelerometers, and Gyroscopes

Motion sensing refers to measuring the spatial bearing, linear motion, and rotational movement. Here are a few examples:

-         A motion sensor in the Nintendo Wii controller (called Wii mote) can detect the movement of hand and allows a game player to play simulated games of tennis, golf, boxing, etc.

-         Motion sensors in smart phones such as iPhone can detect the orientation of the phone with respect to gravity and change the format of display (landscape vs. portrait) when a user holds the phone differently.

-         Gyros in iPhones measures the rotation speed, allowing users to play interactive games such as simulated car driving – a user simply rotate the device to simulate the action of turning steering wheels.

Today (2010), there are two major classes of motion sensors: accelerometers which measure linear acceleration, and gyros which measure rotation speed. The technologies for these two are deeply related but of course not exactly the same. In this article, we discuss them interchangably.

Figure 1: Gyros (rotation speed sensors) allows an iPhone app JetCar to simulate driving a car by using the phone itself as a steering wheel.

A review paper by Prof. Walters provides a very detailed account of the development of accelerometer. (Citation provided at the end of this section. Do a web search with the terms “history of accelerometer walters” to find the article). It is believed that the first accelerometer was made in 1920. The first devices were based on resistance-bridge of carbon resistors. This device weighted a pound. Later, around 1938-1941, bonded metal resistance strain gauges are developed. However, such devices suffer from signal-to-noise ratio issues.  Later, piezoelectric accelerometers were developed. Such devices were used in vibration monitoring for space and air force programs.  Around 1960 Walter Kistler established Kistler Instrument Company to commercialize piezoelectric sensors. Endevco was formed in 1947 in Pasadena, California and commercialized accelerometer in 1951. Endevco focused on microminiature, high shock, high temperature accelerometers. It also pioneered diffused semiconductor strain gauge in 1967.  

Around 1960-1975, a number of companies start to take advantage of diffused silicon resistors for acceleration sensing. These include Fairchild, IC Transducers, Kulite, and National Semiconductors. Kulite was founded in 1959 as the first commercial source of bare silicon strain gages.  National Semiconductor was founded in 1959 by Dr. Bernard J Rothlein after leaving the Rand Corporation (which is founded in 1910 as the Sperry Gyroscope Company by Elmer Ambrose Sperry). In 1982, National Semiconductors exited the sensors business. Around 1983, a new group of sensor companies were formed, after the bulk silicon micromachining process development.  These companies include IC Sensors (1983) and Nova Sensors (1985).

Before 2006, MEMS motion sensors were exclusively developed for the automotive market (crash sensor). The typical volume demand is on the order of tens of millions per year. In 2006, the five major suppliers of accelerometers are Freescale, Analog Devices, Bosch, VTI, and Denso. The leader of automotive MEMS is Bosch, with overall revenue of $457M (M means million) in 2007 and $429M in 2008.

The MEMS sensors business was already a business in 2006. However, it is about to get bigger. In fact, it is predicted to grow so fast that it will overtake the current MEMS revenue leaders – Texas Instrument DLP and Hewlett Packard ink jet printer heads. Why?

In 2006, three things happened:

-         Low cost of MEMS: the MEMS field, after over 15 years of active research and production, is finally able to make motion sensors for less than $1 each;

-         Growing consumer electronics (CE) market: the CE market exploded, with innovative products such as gaming, smart phones, etc.  This is the result of multiple factors, including consumer habit. The Internet infrastructure is fully innovated and people’s use of Internet starts to change (Web 2.0), making portable CE devices highly practical and desirable. Consumers appetite for new electronics gadgets increased dramatically.

-         CE and gaming manufacturers seek differentiation and growth. The CE devices need new human-computer interface (HCI) devices because of their small sizes. Traditional mouse and keyboard are no longer suitable for such platforms. Traditional gaming companies also enter stagnant growth and wants to have new game titles in their business pipelines.

2006-2008 was a turning point for MEMS industry, because of the booming of smart consumer electronics and mobile electronics, which themselves are contributed by the maturation of microelectronics industry (CPU, hard drives, memory, display). The success of motion-based products – Nintendo Wii (released Nov 19, 2006), Apple iPhone (January 9, 2007), and Google Android based smart phones (released Nov 5, 2007), changed the landscape of MEMS motion sensors.  (In fact, these phones changed the landscapes of MANY industries). Apple iPod becomes the first smart phone product to use gyros. However, the iPod only opens up people’s mind about the potential market.  Android phones and future generation of smart phones have much bigger consumer followings. As the price of some MEMS sensors dips below a dollar, every smartphone vendor is scrambling to match Apple's sensor complement.

Even in a generally favorable climate, it still takes tremendous vision, technical skills and courage to succeed. Companies that took advantage of the CE market boom, innovate boldly in time, and bet heavy on the trend, starts to become leaders. For example, in 2008, STMicroelectronics, a company that only started to make accelerometers in 2006, takes a lead in accelerometers for consumer electronics market. By September 2010, ST has made over 850 million accelerometers and gyroscopes!

2008 is also the same year that sales from CE outpaced automotive applications. The sales are now driven by smart phones. Automotive applications account for 40% of global accelerometer revenue in 2008, down from 78% in 2006. In the same period, the revenue from CE applications of accelerometer rise from 22% to 58%.

The growth of CE will lift revenue of MEMS field in general. Global revenue for MEMS devices in cell phones will increase to $1.3b by 2012, up from projected $1 b in 2011, $ 821 m in 2010 and $299m in 2007. The MEMS-for-cell phone market is expected to be $2 b in 2015.

Compared to accelerometers, gyroscope is a new entry. The gyroscope market is growing fast in a number of application segments. In addition to automotive electronic stability systems and GPS receivers, MEMS gyroscopes took off in the consumer segment around 2007, including computer game controllers (e.g. Nintendo Wii), motion-user interfaces in portable communication devices and image stabilizers in camcorders and digital cameras. Analysts expect the total available market for MEMS gyroscopes to grow from $400 million in 2006 to more than $1.2 billion in 2012.

The price drop is significant, and the application volume increased.  A major catalyst for the rise in accelerometer sales is pricing. The price of accelerometers goes below $1 in 2008, making it attractive for a large number of products. Pricing and volume is a chicken-egg problem. Pricing and volume, which is the chicken and which is the egg?

A happy marriage between MEMS and CE goes like this: because MEMS is cheap enough, CE vendors starts to incorporate them in units – the units are large volume demand, very well suited for the MEMS industry. In fact, MEMS has a difficult time dealing with small volume and high cost – high volume CE application seems to be a natural fit.  The large demand drives down the price, which further make MEMS more suitable, and make more CE vendors and consumer want more MEMS products. On paper, having pressure for unit pricing is not good economics for the MEMS industry. Many MEMS companies would secretly admit they love to make more money per unit. However, the price drop opens new, often unexpected market and in turn grows the field in previously unestablished new application arena.  

It is fair to say that the MEMS field and the consumer electronics field is symbiotic – mutually beneficial and growing together.

The dynamics between MEMS chip manufacturers, chip packaging factories, and system manufacturers are blurring. The line between electronics and MEMS is blurring.

Sensors that draw low power and have built-in intelligence will be major trends in future. MEMS Chips are becoming more circuit and computing oriented, whereas IC chips and computers are increasingly becoming MEMS-augmented. In the next five years, the following trends will fully play out:

-         MEMS foundries will mature and able to handle large volume production of complex products;

-         MEMS will become more intelligent by incorporating growing degree of circuit sophistication;

On the other hand, integrated circuit companies will start to innovate in the MEMS space. 

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