Fabrication of high temperature surface acoustic wave devices for sensor applications

Abstract

Surface acoustic devices have been shown to be suitable not only for signal processing but also for sensor applications. In this paper high temperature surface acoustic wave devices based on gallium orthophosphate have been fabricated, using a lift-off technique and tested for high frequency applications at temperatures up to 600• C. The measured S-parameter (S 11 ) has been used to study the mass loading effect of the platinum electrodes and turnover temperature of GaPO 4 with a 5• cut. The analysis of these results shows that the mass loading effect can be used to predict the desired resonant frequency of the SAW devices. Also two different adhesion layers for Pt metallisation were studied. Our results show that Zirconium is a more suitable under layer than Titanium.

High-temperature 434 MHz surface acoustic wave devices based on GaPO/sub 4/

“…For good adhesion between the Pt and the GaPO 4 wafer, titanium (Ti) and zirconium (Zr) underlayers have been tested. Long-term measurements at 600 • C showed that Ti underlayer was not stable at such temperatures [8], and improved results described in this paper have been obtained using Zr. The summary of all metal properties used for the fabrication of SAW devices is shown in Table II.…”

Piezoelectric materials for high temperature transducers and actuators

“…Piezoelectric sensors have been proven to offer excellent resolution, temperature stability, sensitivity and low cost integration properties compared to the other devices for measuring charge, voltage and frequency dependent mechanisms [1,2]. To this end piezo-based sensors, actuators and transducers make up a significant and growing [$15bn market, being widely used throughout a variety of industries from ultrasonic motors and pumps, optical image stabilization, automotive fuel injection, industrial condition monitoring and acoustic non-destructive testing.…”

“…Significant work has been undertaken on developing high temperature single crystals [1,7] such as quartz, lithium niobate [8], langasite [9] and gallium orthophosphate [2] to achieve extremely high temperature stability and operation, but typically suffer from high production costs, low mechanical strength and very low piezoelectric activity which limits their use as replacements to PZT transducer elements in the \600°C range.…”

Platinum–zirconium composite thin film electrodes for high-temperature micro-chemical sensor applications

“…In addition, these noble metal films have found applications in high-temperature sensor applications as the elements for micro-hot plates and electrodes for structural monitoring sensors and thermocouples for harsh-environment energy applications (such as gas turbines and fuel cell systems operated at >500 • C) [6][7][8][9][10][11][12][13][14][15]. Moreover, these noble metal films are also utilized to produce embedded electrodes within various electrical components, where chemical and microstructural stability is required during the thermal processing steps; examples of these include low-temperature co-fired ceramic (LTCC) microelectronic devices and multilayer piezoelectric/electrostrictive actuators and capacitors [16][17][18][19][20][21][22][23][24].…”