Date: 14/10/2012

MEMS: Small improvement in performance cause big change in applications

MEMS is a such a small device, every bit of fabrication happens in either micro or nano-meter scale. The MEMS devices are made using expensive etching tools. The precision at which MEMS can sense depends on the motion precision of nano-sized moving elements inside MEMS. Achieving motion precision is engineering –craftsmanship, the MEMS engineers have achieved improvement in performance over the years by continuously redesigning and tuning the performance of MEMS fabrication equipment which is very similar to semiconductor IC fabrication equipment. It’s not just about achieving precision in one device; it’s more about achieving precision in mass scale. Another important trend is integrating semiconductor IC and MEMS in single package using less-expensive process.

One of the leading companies in MEMS domain is ST Microelectronics. ST is putting complex multiple MEMS and analog and digital ICs in single package. This writer recently talked to Fabio Pasolini, General Manager of the Motion MEMS Division in STMicroelectronics to learn the application trends and technology improvements in MEMS domain. Below are some of the points he shared with me.

The small improvement in performance of MEMS results in bigger expansion in applications of MEMS resulting in market growth. On the emerging applications of MEMS, Fabio Pasolini says “we see the creation of new wave of applications that are location based applications, the internal navigation, the virtual realty where the health monitoring or remote health monitoring and image stabilization, these are the applications that we see in the market in big volume in the coming six months to one year and these applications I will explain you why they are now possible and they were not possible few months ago. They are leveraging on the improved level of performance of the devices which are now hitting the market.”

“In two to five years, sensor that are spread in the environment, that are able to measure characteristics of the environment where we live to communicate this data to a server.” He adds.

On the technical-performance improvement Mr. Fabio says “With old component we were able to recognize the inclination or the orientation in the space in object with a resolution of 1 degree. So we could go at best of 1 degree each. Now we have in the market component that has a resolution of 12 bit and in some case even better reaching up to 14 bit. So this means that from 8 to 12 and then to 14 bit, we have the capability to go with resolution to back up 1 G.”


The domination of Silicon in MEMS:

Mr. Fabio says “The silicon is a good material from a galvomechanical and thermoelectrical point of view and it is compatible with the big volume manufacturing of the types of electronic industry.”

“We are manufacturing and delivering to the market more than 3 million pieces of motion MEMS per day. To be able to reach this kind of level and to stay this increasing demand from the market, it is key to add a manufacturing machine that is compatible with any volume manufacturing and there is no industry that is able to manage or better the volume than the microelectronics industry. So the typical material that the microelectronic industry is able to manage are the silicon wafer.” He adds.

Size and power consumption trends in MEMS:

Fabio Pasolini: This is another good point that I would like to throw light because if we take the evolution of the package from a point that in the beginning we at a footprint of 7 x 7 mm and 2 mm of thickness, it is roughly 100 cubic millimeter, today for the same component for the same function, the component is able to measure 2 x 2 mm with only 1 mm thickness. So we went 100 cubic millimeter to 4 cubic millimeter, shrinking the volume effectively by 25.


Fabio Pasolini: If we look at the previous we went to current consumption in the range of 5 to 10 milliampere, now we are in a situation where our component are consuming 5 to 10 microampere. So we have been shrinking the power consumption by 1000 times.


On the MEMS usage in medical, Mr. Fabio says “Yeah the MEMS, the software plus technology to sense are becoming like a kind of virtual doctor that is always present and we are able to treat the people and to take care of the people while the people are at home and not in the hospital.”


One example of ST’s innovation in MEMS fabrication: ST’s LPS331AP pressure-sensing device is fabricated using a proprietary MEMS technology, called “VENSENS”, that allows the pressure sensor to be fabricated on a monolithic silicon chip. Manufacturing the device in this way eliminates wafer-to-wafer bonding and maximizes reliability. The sensing element in the LPS331AP is based on a flexible silicon membrane formed above an air cavity with a controlled gap and defined internal pressure.
Author: Srinivasa Reddy N