MEMS World: Design, fabrication, applications

MicroElectroMechanical Systems: an evolution of microtechnology

Microtechnology has offered Microelectronics, which has completely changed our way of life. Microelectronics is omnipresent in everyday life: at home, in our computers, our dishwashers, our cars, etc. Its applications are able to help us, take care of us, control things for us and much more! But now a new way of using microtechnology has risen. By including mechanical movable parts in integrated devices, the microactuators, we have opened a window to an extremely large applications fields. These new devices involving mechanical and electrical parts capable of acting on and sensing their environment are called MicroElectroMechanical Systems (or MEMS or Microsystems). Not a technology revolution, MEMS are more an evolution, that has taken place in our life, and will become more and more important.
This section features microactuators basics, for design consideration, including electrostatics and MEMS based on thermal actuation, a sample micro-fabrication process, and describes MEMS commercially available applications that our current know-how allows.

Introduction

MEMS can be defined as the combination of microsensors and/or microactuators and electronic devices integrated on a single chip.
This means that you're supposed to have a black box, that is the package, a bit like processors, but it includes all the mobile parts of the device. This is sometimes the case, but sometimes, you can find under MEMS call one or more actuator(s) in a single chip, and the associated electronics is to be placed separately.
MEMS rely on the same technology that have given microelectronics devices. It consists in deposit and etch material layers to give them the shape and properties you need. The differences are that MEMS use a lot of different materials, and that due to the very large functions to be achieved, you can almost consider that there is one fabrication process per existing device.
The second large difference between microactuators and microelectronics fabrication is the sacrificial layer. As microfabrication is done by surface fabrication rather than by making each piece separately, you need a layer that is to be removed at then end of the process to free mobile parts.

The MEMS term and the other ones

There are several different word to design Microelectromechanical Systems (MEMS). In fact, the acrony MEMS is rather used in United States, and has spread around the world. Japanese people historically talk about micromachines while european people say microsystems.
The origin for this different terms lies on the approach of the disciplin.
For japanese, the main idea was to have the same machines as found at macroscopic level, but as small as possible. So the term micro-machines represents this point of view.
In United States, the goal was to get... exactly what is suggests! By using microelectronics fabrication process, making movable mechanical parts powered by electricity that achieve a function.
In Europe, the original approach was more focused on making a real system, combining mechanics and advanced electronics. In fact, you could consider that a microsystem is the combination of a MEMS and its associated electronic treatment device.
Of course, right now, the different approaches have merged! Microtechnology principles are the same for everyone, and the term MEMS is dominant as it is probably the most appropriate term for what is actually done.
There is a last term that has almost never been used: micromechatronics. Mechatronics is originally a system combining mechanical and electrical parts, but used together in a very integrated way, including at automation design level. This is supposed to be more than just an actuator driven by an electronic device. But at the time I write this page, considering what we make as micromechatronics is a bit presomptuous, though this will be the final goal.
So, let's stay with the MEMS term!

Summary

In the following sections, I will try to show you what MEMS are, how they've been emerging, what kind of applications already exist, and which are the next ones to come. I've also included a sample microtechnology process for a very simple device. And I introduce the different principles used in actuators design.
I plan to add later pages about sensors, microfluidics devices, MOEMS (for Micro OptoElectroMechanical Systems), and BioMEMS. Thanks to be patient!!