Erik Ansorge

Plano-Convex Shaped Langasite Microbalances for High Temperature Applications

Piezoelectrically actuated plano-convex thickness shear mode (TSM) resonators in lanthanum gallium silicate (langasite) were fabricated. As main fabrication steps a wet etching process and a dry etching process were developed and furthermore graytone-lithography in combination with photoresist melting has been applied. The plano-convex shape is necessary to improve the Q-factor of the devices. The resulting Q-factor was up to two times higher than for simple planar resonators reaching values of more than 60,000. The special characteristics of langasite allow working temperatures of more than 700degC and a sensitive CeO2 coating can be used for gas measurements at high temperatures.

Microelectromechanical structures in langasite (La/sub 3/Ga/sub 5/SiO/sub 14/) by wet chemical etching

Lanthanum gallium silicate (langasite, La/sub 3/Ga/sub 5/SiO/sub 14/) is a new piezoelectric material with promising properties for micro-electromechanical applications at high temperatures. So far it has been used for SAW and BAW devices. This paper reports on the possibility of fabricating microstructures in langasite by wet chemical etching. The etching behavior of different chemicals applying different mask materials was investigated. Further, the effect of doping on the etching behavior was studied. As a first demonstrator a cantilever beam in langasite has been produced showing the possibility of MEMS in langasite. The resonance spectrum of this device was recorded at temperatures up to 600/spl deg/C.

Gas detecting langasite membranes by wet chemical etching

Piezoelectrically actuated membranes in lanthanum gallium silicate (langasite) were fabricated. The membranes have shown operating temperatures up to 850 degC and are applied as high temperature gas detecting devices by means of CeO2 sensor films. The measurements show, that gas sensing with membranes is feasible and results in even higher frequency shifts as for thick plan-parallel resonators. A multi-step wet chemical etching process has been developed and was used to structure the langasite. Furthermore, membranes have been fabricated by using the different etch characteristics of doped and undoped langasite

Miniaturized resonant gas sensors for high-temperature applications

The application of bulk acoustic resonators as gravimetric sensors enables high-temperature gas sensing provided that (1) the materials used withstand high temperatures and (2) the transducers are highly sensitive and selective. The former is realized by application of the high-temperature stable piezoelectric material langasite (La3Ga5SiO14). The focus of this work is the improvement of the sensitivity and selectivity by application of microsystems engineering methods to machine membranes. First, appropriate designs to achieve high resonator quality factors and low thermal stress are developed and realized by machining of biconvex membranes and monolithic electrodes, respectively. Further, the thickness of membranes is as little as about 25 mum thereby leading to high mass sensitivities. The concept is proven by successful operation of langasite membranes at temperatures up to 900degC. Membrane arrays wearing different sensor films are shown to improve the gas selectivity at 600degC.

Design and fabrication of high-Q langasite resonator arrays for high temperature applications

The design of piezoelectrically actuated plano-convex shaped resonators in lanthanum gallium silicate (langasite, LGS) was investigated and improved by finite element simulations. Especially effects of shape and clamping were simulated. Further, devices that demonstrate the working principle have been fabricated. The membrane arrays have shown operating temperatures of more than 700degC and are applied as high temperature gas detecting devices by means of CeO2 sensor films. The special shape of the resonators causes an energy confinement and improves the quality factor at high temperatures. Wet etching, dry etching and masking technologies had to be applied for the fabrication. Simulation results could be confirmed by measurements.

Piezoelectrically driven spherically contoured resonators in LGS for high temperature applications

Piezoelectrically actuated plano-convex thickness shear mode (TSM) resonators in lanthanum gallium silicate (langasite, LGS) were fabricated. As main fabrication steps a wet etching process and a dry etching process were developed and furthermore graytone-lithography in combination with photoresist melting has been applied. The plano-convex shape is necessary to improve the Q- factor of the devices. Simulations have been run to show the influence of the spherically contoured surface. The resulting Q-factor was up to two times higher than for simple planar resonators reaching values of more than 60.000. The special characteristics of langasite allow working temperatures of more than 700degC and a sensitive CeO2 coating can be used for gas measurements at high temperatures.

Fabrication and test of arrays of langasite microbalances

The design of piezoelectricaly actuated plano-convex shaped resonators has been studied to optimize their Q-factor and signal spectrum at high temperatures. The investigated arrays of thickness-shear-mode (TSM) resonators consist of langasite, a high temperature stable material. As viscoelastic damping and an increasing conductivity decreases the Q-factor at elevated temperatures, design optimizations have to counteract these effects. Two and three dimensional finite element (FE) models have been solved to analyze the resonant behavior and the effects of energy confinement at different temperatures depending on geometry. The separation and suppression of spurious modes, the improvement of the Q-factor and the confinement of the TSM could be shown. The simulated effects of energy confinement could be proofed by impedance measurements.

Modeling of energy confinement of plano-convex shaped resonators for applications at high temperatures

The design of piezoelectricaly actuated plano-convex shaped resonators has been studied to optimize their Q-factor and signal spectrum at high temperatures. The investigated arrays of thickness-shear-mode (TSM) resonators consist of langasite, a high temperature stable material. As viscoelastic damping and an increasing conductivity decreases the Q-factor at elevated temperatures, design optimizations have to counteract these effects. Two and three dimensional finite element (FE) models have been solved to analyze the resonant behavior and the effects of energy confinement at different temperatures depending on geometry. The separation and suppression of spurious modes, the improvement of the Q-factor and the confinement of the TSM could be shown. The simulated effects of energy confinement could be proofed by impedance measurements.