New high temperature SiC mass sensors based on electrostatic resonator structures are developed using FLASIC material. The maximum working temperature is 300?C. These type of sensors can be used for gas detection or molecules identification. Similar sensors have been developed by CNM and other labs on Silicon. The main advantage of the new sensors developed with FLASIC material is the higher performances (resonance frequency, resonance amplitude, quality factor) due to the higher young modulus of SiC compared with Si.
To fabricate these devices, several technological processes have been set up with especial emphasis on deep SiC etching. Optimal etching condition with ICP has been found to obtain good etching rate, without damaging the Aluminium mask and maximizing the etching selectivity. With these new conditions, lateral cantilevers with widths down to 1um and a thickness of 2.5um have been obtained. This is a relevant technological result that can be also used for the integration of other type of devices in 3C-SiC on Si. Doping and contact formation on the SiC layer, needed for the full electrostatic sensor, have been also developed and optimised. In addition, SiC membrane formation process has been set up using backside-processing technology for Si removal. This process can be used for the fabrication of freestanding resonators for gas detection or for pressure/accelerometer sensors fabrication on SiC membranes.
The targeted applications have a strong environmental impact. For example, in the case of gas sensors, it is aimed at the control and regulation of the gases exhaustion regimes. The energy transformation resulting from the burning process can be optimised in order to obtained a maximum efficiency and a limitation of gases rejected in the atmosphere. Other applications can be contemplated in the automotive field as well as in Aerospace applications. In a similar way, the efficiency of the internal combustion engines or reactors can be regulated and improved using information given by the exhaust gas sensing. This may allows reduction of fuel consumption.
The main potential barriers are the long-term reliability validation of the sensors and the availability of a high temperature package for housing the sensors in the final application systems. Prototypes of impedance needle sensors have been also fabricated. The results on bulk SiC are very attractive and future commercialisation could be contemplated in the next 24 months. Fabrication of needles on Flasic material has to be optimised but is attractive due to its lower cost.