MINATEC

MEMS technology for the sensor manufacturing is widely spread, for example in automotive industry (accelerometer for airbag), or, more recently in consumer market with gaming systems. For these applications, sensors must be cheaper and cheaper, that means smaller and smaller, and integrate more functions without lowering their performances. However, an homothetic sensor size decrease inevitably induces a resolution decrease.

MEMS technology for the sensor manufacturing is widely spread, for example in automotive industry (accelerometer for airbag), or, more recently in consumer market with gaming systems. For these applications, sensors must be cheaper and cheaper, that means smaller and smaller, and integrate more functions without lowering their performances. However, an homothetic sensor size decrease inevitably induces a resolution decrease.

Today, we are developing in our lab a technology named M&NEMS which allows disconnecting the sizing of the detection part (piezoresistive gages) with nanometric dimensions from the inertial part with micrometric dimensions. So, a size reduction without affecting the performances is possible. We are using it to develop accelerometers, magnetometer and gyrometer. We propose a PhD thesis to explore the possibilities given by this technology to conceive, manufacture and characterize another type of sensor for measuring a force along 3 axes (X, Y and Z), with buried nano-gauges and rear face contacts.

Besides the extreme miniaturization of this device combining MEMS and NEMS, this concept and this technology M&NEMS using nanofil type suspended piezoresistive gages has several advantages:

• A very high sensitivity given by the stress concentration in gauges with nanometric section

• The possibility to increase this sensitivity taking advantage of the giant piezoresistive effect observed in silicon nanofils with diameter lower than 100nm

• The possibility to have a sensitivity along 3 axes with a single device (CEA patent)

• The possibility to use this component in harsh environment because of buried (so protected from external environment) and suspended gauges (so able to withstand high temperatures contrary to implanted gauges)

• The possibility to have rear face contacts, which simplify the interconnection in case of sensor network

This 3D force sensor is a candidate for several applications for example in haptic domain (touch sensing), for medical applications (anti-bedsore mattress), industrial control (non destructive texture analysis for cosmetic, food industry…) or robotic.

The conception and sizing of the sensor, from analytical equations and finite element modelling, will take into account the specifications and the technological design rules. The layout will then be defined and the PhD student will insure the fabrication control in cleanroom. The device will then be characterized and the results compared to the theoretical expectations. A special attention will be paid to the giant piezoresistive effect which will be investigated from a theoretical and experimental point of view. The PhD student will conduct his work within an about twenty person team and will benefit from the LETI technological means.