The MEMS revolution

Benedetto Vigna / Executive Vice President, General Manager of MEMS & Sensors Group, STMicroelectronics / 2014-10-11

MEMS are basically information sensors that transmit the information to a microcontroller that carries out the analysis. It is an essential element of the so-called smart objects, allowing them to capture information about their environment. MEMS are to the world of smartphones and tablets what transistors were to consumer electronics in the 1960s. They’re everywhere! A series of technological breakthroughs and industrial gambles paved the way to a flourishing market. Benedetto Vigna is one of the leading figures of this revolution.

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ParisTech Review – First things first: what exactly are MEMS?

Benedetto Vigna – I could answer your question simply by explaining what the four letters of the MEMS acronym stand for: a micro-electromechanical system. This mechanical system of very small size (a few square mm) is made of silicon in most cases and has at least one micrometric component. They are used as a sensors or actuators. Some MEMS react to atmospheric pressure, others to moisture, altitude, heat, movement (acceleration for an accelerometer, rotation for a gyroscope and magnetic field for a magnetometer), light or sound…

In less than a decade, they have become fundamental components of most high-tech products that surround us. We can no longer do without. Today, a smartphone contains up to 10 MEMS!

Less than a decade? But the first models were developed in the 1980s.

And even in the 1970s. But even though they hit the market in the 1980s, they gained momentum during the twenty-first century. This story is worth the telling.

You’re not wrong to evoke the 1980s, since that was precisely when we started to use them in the industry. Inkjet printing heads, for example, use MEMS; airbags implemented inside our cars are triggered by an accelerometer whose central component is an MEMS. All these objects were developed in the 1980s and 1990s, at a time when miniaturization progressed quickly.

But the revolution took place in the 2000s and was triggered by a much more trivial object: a video game console! As you might have guessed, I’m talking about the famous Nintendo Wii fitted with a system capable of detecting the position, orientation and movement in space. The Japanese manufacturer spotted this idea on a lounge where STMicroelectronics – at that moment, an outsider in the market for microelectromechanical systems – was presenting a motion sensor. We started working together in 2005 and the game console was released in 2006. Its success was huge and the work undertaken with Nintendo has allowed us to establish ourselves in an emerging sector, that of smartphones. Because without MEMS, there wouldn’t be any smartphones. You could have sophisticated phones, coupled with small computers, but you couldn’t drag your fingers on the screen and the screen wouldn’t rotate automatically thanks to an integrated accelerometer. And that’s not all: if your smartphone is as comfortable to use during phone conversations, it’s because it has one or two MEMS microphones to capture your voice and one or two other MEMS microphones to capture ambient noise and cancel it. Smartphones aren’t only made of computer components: they’re also equipped with sensors which transform them into the perfect connected device, not only to the network but also to their environment.

This dimension will get increasingly important. Tomorrow, onboard sensors will convert smartphones into portable weather stations, capable of measuring humidity, atmospheric pressure, air quality, UV index… and combine these data based on network sources to refine their predictions.

That’s clearly more than the first models that reacted only to movement or light…

Indeed, and this is where the comparison with the transistor is no longer relevant. A transistor, even if we transform its components, is still based on the same structure and the same function. While MEMS are a growing world with changing structures and ever-increasing functions. Initially, they come from the world of micro-electronics and their sensing functions were originally confined to mechanics and optics. But this is no longer the case: many other disciplines are involved now.

ITs play a very important role as there is increasingly more information to sort and to transmit. Besides, the quality of this information is crucial. Chemistry and biology are also involved because the captured information isn’t only a light wave or a mechanical movement. It can also be a presence detector or a chemical or biochemical dose. Biology and medicine are very important users of MEMS, and this phenomenon will increase, especially with the development of techniques for remote monitoring or personalized medicine. These MEMS of a new kind are sometimes called bioMEMS.

In the same way that the disciplines involved are not limited to electronics, the materials used have evolved too. What’s still electronics is the use of electricity. But even though MEMS are often based on silicon, they also use metal, piezoelectric materials and even polymers. Depending on the desired applications, a particular material will be chosen based on its physical properties: its sensitivity, the accuracy of its reaction, its frequency of use, etc.

A flat micro-gyroscope

How are they manufactured?

That’s part of our technological secrets! They are protected by hundreds of patents… But the principle is simple: an MEMS is a substrate – usually silicon, but not only, as mentioned earlier – and it has a moving part, a tiny mechanical mechanism (such as a resonator or a micromotor, etc.).

To work on the substrate we use the same technologies as in microelectronics: patterning, photolithography, wet or dry etching. The main singularities of MEMS production technologies, compared to microelectronics are due to the manufacturing of the moving parts, generally obtained by using what a so-called “sacrificial layer”. When MEMS work, mechanical components are actuated by the forces generated by electromechanical transducers supplied by the voltages produced with neighboring electronic circuits. These transducers work as an interface between the electrical and mechanical domains. A sensor operates exactly in the opposite way: for example, an acceleration or a rotation create a force which causes the displacement of the moving part; by measuring the variation of distance between the fixed and moving part, the value of the acceleration (accelerometer) or of the rotation (gyroscope) can be deduced; capacitance is used: between two electrodes (a fixed one a mobile one), when the distance increases, capacitance decreases and when the distance decreases, capacitance increases; the ability to measure the capacitance allows to measure the distance and therefore the implemented force.

The reliability and accuracy of this interface are fundamental. That’s what really counts. If your smartphone crashes, it’s a minor problem. But MEMS used in aerospace and medicine need to be absolutely reliable: human lives depend on these tiny devices. And thanks to these stringent requirements, your smartphone works very well!

Let’s talk about their applications. What are the mostly used for today?

Apart from accelerometers and other applications installed in smartphones, which we mentioned earlier, there are also analogue or digital micromirrors that define the pixels of some projectors; microfluidic control valves and pressure sensors; electromechanical filters that isolate a frequency from an input signal…

To give you an idea of the quantities involved, in early 2013, a company like ST Micro had already produced three billion MEMS. And while we are the leader of the MEMS market for mobile and consumer electronics, there are also other major industrial players targeting other markets. Inkjet heads also represent a huge market, with more than three billion units sold.

Sensors inside a smartphone sold $600 cost $150 to make, that’s quite a few dollars. That’s not a negligible amount. For STMicroelectronics, in 2005, MEMS represented a market of 200 million dollars. Today, they represent a billion dollars.

To give you an idea of the market as a whole, let mention two figures: the market for MEMS for smartphones represents now $6 billion; the MEMS market as a whole is expected to reach $22 billion in 2018.

Gyroscopes’ applications

The market is still new and positions are evolving very quickly. How did STMicroelectronics – an outsider in 2005 according to your own words – become one the leading international companies?

Back then, we made an industry gamble by doubling the size of the “slices” on which components are machined: we went from 15cm to 20 cm in diameter without any quality loss. This helped us increase drastically our production and reduce costs. The rest is a matter of responsiveness, reliability, ability to keep the pulse of the market and offer innovative features. These are the qualities of an outsider, which we managed to preserve so well that we are now the worldwide leader – and by far – of MEMS market for consumer electronics.

One must understand that this segment is driven by a truly exceptional dynamics of innovation: all kinds of applications appear and many sectors invest in our technologies. For example, the automobile industry, one of the first industries to use MEMS for airbags, began applying them for other features such as support systems for parallel parking. The health sector and more generally, welfare technologies, are also very important users: all the innovative instruments that allow you to measure your blood pressure while you walk or your diabetes at home will be using MEMS. The demand is exploding, and industry players such as STMicroelectronics spend 15-17% of their revenues in R&D.

For this kind of high-tech products, there are several schools: some players focus on in-house innovation; others respond to requests for an ecosystem from client companies, including startups; others invent products and then seek partners to imagine their uses – for example GoogleGlass, today. How do you work?

We define innovation as a business process, by which new ideas or inventions mature gradually and provide our customers with differentiating features. For us, innovation must create value both for ST and for the customer. We can work a phase ahead of our customers by taking into account their needs in our specifications. Thanks to our market research, we can also develop circuits that will be highly appreciated by our customers once marketed. In both cases, the value in use is anticipated.

Let’s talk about the future, precisely. What role will the MEMS play and, more prosaically, what direction will the market take?

The “Internet of Things” is already here, and it will require more and more MEMS. Smart objects – just as smartphones today, or connected glasses and watches tomorrow – will rely on an increasingly dense network of sensors that will measure, more or less systematically and very accurately, an increasing number of parameters in a given environment. Both internal parameters (your blood pressure, oil level of your car) and external ones (humidity, sunshine).

MEMS will extend to domestic uses, thanks to home automation, mobility in all its forms, but also to the city of tomorrow. There is much talk about smart cities. These cities are based on a refined monitoring, and therefore an improved management, of flows – especially in the field of transport of people and goods. Sensors are crucial to measure these flows and feed centralized computer systems that will modulate them.

But they can also, more modestly, help manage a street: lampposts in a smart street will light up only if needed, will respond to the human voice (and make the difference between ambient noise and the barking of a dog for example) or to a command (these will require a sensor capable of differentiating “fiat Lux” from “the weather is cool”) or to a movement (making the difference between a human and a lost deer). MEMS are therefore part of the nervous system of smart streets and by providing accurate information, they contribute to their intelligence. Imagine a street that understands that you’re shouting and alerts the police! Well, that’s for tomorrow.

To go even further, one can easily understand that the smarter the sensors, the smarter the street, the city or the car that will use them. That’s why the market is moving today towards integrated solutions, MEMS capable of integrating and digesting complex information, like computers.

Another avenue for evolution is augmented reality: earlier, I mentioned portable weather stations, but other possibilities emerge and the launch of the GoogleGlass should give a decisive impetus to this market. MEMS are already playing a key role in enhanced video – they allow your kid to be part of his own video game… If you are lost in Kuala Lumpur and don’t have a map, you only have to tell your smartphone: “I want to go downtown” – and get there in fifteen minutes. Today, most of these functions are associated with smartphones, but by 2020 smartphones will have changed. What defines them today will be dissolved into other objects. Your clothes, for example.

In 2020, even an apple will be smart: it will be equipped with one or more sensors that will measure its taste or maturity and will alert your refrigerator that it has to be eaten. In any case, the information will reach you: the humanization of technology is one of the major trends in recent years in the field of microelectronics. This is precisely what has contributed to the success of smartphones, simplicity coupled with extreme sophistication; increasingly accurate and varied information and at the same time, simplicity of use. And believe me, you still haven’t seen anything.