P. Argyrakis

Dry etch release processes for micromachining applications

The authors report on the comparative study of two dry etch processes for polysilicon sacrificial layer release using vapor phase xenon difluoride (XeF2) continuous etching and inductively coupled plasma (ICP) etching with sulfur hexafluoride (SF6) gas. Test structures of 0.5μm thick polysilicon have been patterned and etch channels varying in widths from 1to500μm have been fabricated successfully for the purpose of comparison. The influence of etch pressure, aperture opening size, and ICP etch power on the undercut etching rate as well as selectivity between mask and substrate have been studied. It has been possible to achieve an undercut etch rate of up to 11.6μm∕min under a pressure of 3Torr in XeF2 etch gas, while for SF6 plasma, an undercut etch rate of 2.56μm∕min at 65mTorr is obtained. Moreover, the optimized process has been employed for the fabrication of silicon carbide (SiC) resonators.

Relaxation of process-induced surface stress in amorphous silicon carbide thin films using low energy ion bombardment

The surface stress in amorphous silicon carbide (a-SiC) thin films has been modified after processing. We show that low energy argon ion bombardment in an inductively coupled plasma reactor causes relaxation of the induced surface stress. Cantilever beams of variable length (25–150μm) have been fabricated and their deflection profiles have been compared before and after ion bombardment using white light interferometry. Our experiments show that the ion bombardment relaxes the stress gradient of the cantilever beams. Both the duration of plasma exposure as well as the bias voltage contribute to relaxing the stress gradient in the a-SiC thin film.

Integration of wind sensors and analogue VLSI for an insect-inspired robot

We have designed an adaptive analogue VLSI neuromorphic chip that will be used to interface MEM wind sensors to an insect-inspired robot. The main chip components are a sensory interface circuit to amplify the signal from the MEM device, and integrate and fire neurons with adaptive firing thresholds. The chip has been implemented using Austria Microsystem Systems 0.35µm CMOS technology. We report the response of the prototype sensor to a wind stimulus, and show the neural circuit can reproduce the adaptive behaviour of biological sensory neurons.

Microscale sensors based on silicon carbide and silicon

The current paper consists of two topics related to microelectromechanical systems (MEMS). The first topic reviews recent advances made in the area of silicon carbide (SiC) MEMS for applications in harsh environments. Given the unique properties of SiC, the potential and progress in the development and deployment of the harsh environment material for the fabrication and characterization of resonators and pressure sensors are described. The second topic details the motivation behind the study of biologically inspired systems and how silicon-based microscale sensors with out-of-plane structures could be integrated with analogue very-large-scale integrated circuits (VLSI) for insect-inspired robotic studies.

Design, fabrication, and testing of 3C-SiC sensors for high temperature applications

SiC is widely recognized as an ideal candidate for electronics and sensors required to operate at extremely high temperatures. Cubic SiC (3C-SiC) is preferred to the hexagonal polytypes for the fabrication of mechanical devices due to its lower cost (a film is deposited on a Si substrate) and greater ease of fabrication. As the deposited SiC film is normally quite thin, some traditional designs of devices are not suitable. The Capacitive Ring-Electrode Accelerometer (CREA) introduced in this paper offers much greater design flexibility. Featuring a central boss of un-prescribed thickness, the value of its seismic mass can be set over a wide range, independently of the sensing capacitance. The latter is realized between a SiC electrode, which surrounds and moves together with the boss, and the underlying substrate. The CREA design was extensively analysed in a FE environment and prototypes were fabricated. Pressure sensors based on the deformable membrane principle and piezoresistive pickup have also been designed, fabricated and tested. The dependence of apex displacement on pressure was used to extract the Youngs modulus and the residual stress of the SiC film (bulge test). The membrane was investigated by optical profilometry at various values of pressure and at temperatures between 300 K and 800 K. The shape of the membrane was compared with the FE predictions with a positive outcome.