Page 415 - Microsensors, MEMS and Smart Devices - Gardner Varadhan and Awadelkarim

REFERENCES 395

The output voltage can be calculated for a given Coriolis force, which is determined
by the rotation rate (see Figure 13.33). The gyroscopes were fabricated by both the lift-
off 4 and reactive ion-etching (RIE) techniques using the Pennsylvania State University
Nanofabrication facility. The lift-off technique was adequate for 75 MHz gyroscopes,
which have a minimum feature size of about 6 um.
The response of the SAW gyroscope was evaluated using a rate table. The output
response was measured using an HP dynamic signal analyzer fed by an RF lock-in ampli-
fier. The gyroscope is fixed to a rate table, which, when excited at a constant frequency,
causes the rate table to oscillate, and the gyroscope is measured for each setting. Both the
frequency and the amplitude of the driving signal controls the amplitude of oscillations
of the table, which in turn varies the rotation rate. Figure 13.33 presents the measured
and computed output voltages from the SAW gyroscope for different rotation rate.

13.5 CONCLUDING REMARKS

In this chapter, we have described some of the many sensing applications to which a SAW-
IDT microsensor may be applied. The principles that govern these IDT sensors have been
presented along with the input-output equations. The versatility of this technology is very
impressive and permits a wide variety of different sensing applications, such as strain,
pressure, temperature, conductivity, and dielectric constant.
The next chapter is dedicated to the topic of IDT-MEMS sensors that represent an
exciting development combining the fields of MEMS and SAW-IDT devices. The final
example of a SAW-IDT device is described in Section 15.2 and is associated with a type
of smart sensor called an electronic tongue. It complements the description of another
smart sensor also given in the final chapter called the electronic nose.

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Datta, S. (1986). Surface Acoustic Wave Devices, Ch. 3, Prentice-Hall, New Jersey.

4
The lift-off process was described in Chapter 12.