Integrated GaAs SAW Sensors Acoustic Wave Chemical Detectors and Integrated Microelectronics Fact Sheet |
Figure 1: Comparison of GaAs and quartz SAW sensor response to perchloroethylene, a volatile organic compound. Similar responses indicate that GaAs SAW sensors have comparable sensitivity to quartz devices. |
Applications
The combination of low power, compact size, high sensitivity and robustness makes integrated high frequency SAW sensors ideal candidates for applications requiring miniaturized and portable trace chemical detection, especially those requiring extended deployment in remote or inaccessible locations. Integrated SAW sensor arrays will allow both detection and identification of a vast number of chemical species. In the future, we expect these devices to be employed for:
Figure 2: Photomicrograph of a monolithically integrated GaAs SAW sensor showing the SAW device and oscillator amplifier, This sensor operates at 470 MHz. Changes in the SAW velocity produce changes in the oscillator frequency. |
Figure 3: Comparison of 110 MHz and 380 MHz GaAs SAW sensors upon exposure to two concentrations of perchloroethylene. The higher frequency device is 10 times more sensitive yet occupies one-tenth the area of the lower frequency device. |
The integrated GaAs SAW sensor is shown in Figure 2. It consists of a 470 MHz GaAs SAW device along with a multistage amplifier, forming a monolithic RF oscillator circuit. The amplifier circuit contains 4 gain stages and an impedance matching output stage encompassing 32 transistors. The transistors are fabricated using a standard 0.8 micron gate length metal-semiconductor field-effect transistor (MESFET) process developed in the CCSST at Sandia. Currently, 5 of these devices can be fabricated on 5 mm x 5 mm chip.
Monolithic integration of acoustic sensors and supporting microelectronics leads to a number of advantages including reduced power consumption, reduced size, simplicity of packaging, and more economical device fabrication. By eliminating the need for high frequency interconnections, integration is helping us move to higher frequency devices. As shown in Figure 3, increasing frequency provides enhanced sensitivity and smaller device size. The integrated SAW sensor is compatible with current state of the art SAW sensor coating technology developed for quartz sensors. Future designs of these devices will include:
Ed Heller
ejhelle@sandia.gov
(505) 844-1798
Greg Frye-Mason
gcfrye@sandia.gov
(505) 844-0787
Last modified: August 23, 1999