Transducer consists of a hybrid thin film and a piezoelectric transistor that acts as a stress-sensitive device with built-in gain. It provides a stress/strain transducer that incorporates a signal amplification stage and sensor in a single package

Conragan, J.

Muller, R. S.

English

NASA Technical Reports Server

Jul y
 1970	 Brief 70-10157 
.
NASA TECH BRIEF 
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Piezoelectric Transducer 
Insulator 
Typical Thin-Film IGFET Structure 
A piezoelectric transducer consisting of a hybrid 
thin film and a piezoelectric transistor that acts as a 
stiss-sensitive device with built-in gain has been 
designed. This innovation is novel in that it provides 
a stress/strain transducer that incorporates a signal 
amplification stage and sensor in a single package. 
Most transducers made with piezoelectric materials 
require external amplification and do not produce 
a dc response to an applied strain. By the proper use of 
piezoelectric materials in the fabrication of an 
insulated-gate field-effect transistor (I GFET), how-
ever, a strain transducer can be constructed that per-
forms both the strain-sensing and amplification func-
tions in one integral device. The advantages of such a 
device include both fast response to an applied strain 
and a small, well defined sensing area. In addition, 
a device using a piezoelectric semiconductor will give 
a dc response to an applied strain.
Three basic IGFET configurations can be fabri-
cated with piezoelectric materials. These structures 
involve the use of piezoelectric materials as either the 
semiconductor, the substrate, or the insulator. The first 
two of these uses are the most practical at the present 
time. 
The accumulation-mode device in which ohmic 
contact is made to the semiconductor lends itself to 
fabrication by thin-film techniques on various sub-
strate materials (Ref.). A cross section of a typical 
thin-film device is shown in the figure. The substrate 
can be any insulating material, from a rigid material 
such as glass to a highly flexible polyimide film. Vac-
uum-deposited semiconductor materials that have 
been used in IGFET construction include cadmium 
sulfide, cadmium selenide, and tellurium. The semi-
conductor films range in thickness from 100 A to I 
micron. The silicon-monoxide insulating layer is 
As(continued onrIc.u1) 
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typically 500 A thick, and aluminum is usually used 
as the electrode material. During a study, devices 
were fabricated in which the separation between the 
source and drain electrodes was 0.001 in., while the 
width of the electrodes was 0.1 in. 
Small-area strain transducers can be made by using 
piezoelectric materials in the construction of IGFET's. 
Typical transducers have a stress-sensing area of 100 
sq miis or less, and can detect strains in the range of 
10- to lO-. Although these devices could have re-
sponse times of about 10 nsec, they are presently 
limited to l-1i-sec for the larger area devices. The 
thin-film IGFET strain transducer, which can be de-
posited on a larger variety of substrate materials, can 
be used either as a source of current or voltage by the 
additional deposition of a load resistor using a second 
IGFET as a source follower. These transducers can be 
used in microphones, various strain-instrumentation 
systems, and as surface-acoustic-wave detectors. 
Because of the research in progress, the sensitivity and 
stability of the devices should be improved. 
Reference: 
Conragan, J.: IGFET Strain Transducers Utilizing 
Piezoelectric Materials, Electronics Research 
Laboratory, University of California, Berkeley 
(Audio Engineering Society, Room 428, 60 East 
42nd Street, New York, N.Y. 10017).
Note: 
This innovation should be of interest to manu-
facturers engaged in the fabrication of such 
devices as microphones, hydrophones, and seismo-
graphic instruments. It should also be of interest 
to the designers and producers of thin-film semi-
conductor devices. 
Patent status: 
Title to this invention has been waived under the 
provisions of the National Aeronautics and Space 
Act [42 U.S.C. 2457 (f)], to the Regents of the Uni-
versity of California, 2200 University Avenue, Berke-
ley, California 94720 
Source: James Conragan and Richard S. Muller of
The University of California
under contract to
NASA Headquarters
(HQN- 10548)
L-1 
category 01 Brief 70-10157	 .


Piezoelectric transducer

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