Miniature transducers involve the use of appropriate commercial epoxy resins. Design protects the sensitive semiconductor surface from ambients and excludes an air space in the device capsule

Iannini, A.

Rindner, W.

English

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December 1968	 Brief 68-10563 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Pressure-Sensitive Bonded Junction Transducers 
Top Diode Contact
Hard Epoxy
Flexible Epoxy (Counler)
Chip	 Mesa	 Support 
Pressure sensitivity of semiconductor junctions, 
such as in transistors and diodes, has been a subject 
of extensive investigation. Specifically, considerable 
efforts have been made to develop electromechanical 
transducers based on these piezojunction effects. To 
achieve significant electrical response in these de-
vices, the stress magnitude at the junction must be 
quite large (^! 108 dynes/cm); yet for many practi-
cal purposes the applied forces to which most of the 
transducers must respond are often only a few grams 
or less. An obvious solution is to concentrate the 
applied force over very small areas of the device, an 
approach that has been generally adopted. Generally, 
the desired stress concentration has been accom-
plished by the use of fine, hard styli resting on the
surface of the device and, in one case, by a needle-
shaped semiconductor diode in contact with a flat sur-
face. In these approaches, operation of the device is 
thus based on intimate, uniform contact between a 
minute, hard semiconductor surface and a hard solid. 
In practice, however, it is extremely difficult to main-
tain two very hard surfaces in uniform contact over a 
minute area. Surface irregularities of micron or even 
submicron size will lead to damage in the semicon-
ductor, and it is difficult to prevent lateral displace-
ment of the contact area during operation, or particu-
larly during assembly of the device. 
These problems have been solved by the design of 
miniature transducers which involve the uTse of ap-
propriate commercial epoxy resins. These provide (a) 
(continued overeafl 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States	 information contained in this document, or warrants that such use 
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a means of equalizing the pressure in the 
tact area between the hard stressin g memb 
semiconductor, (b) a support for the deli ----- 
structures exposed to anisotropic stresses, and (c) a 
mechanical linkage. The mesa structure, i.e., a minute 
device surface protruding over the surrounding in- 
active region, is chosen in order to achieve maximum 
stress concentration. The pressure equalization and 
mesa support are provided by a hard epoxy, while a 
flexible epoxy is used to avoid excessive damping in 
the mechanical coupling to the device. Such use of 
epoxies can equally well be applied to tunnel diodes 
as well as to other semiconductor junction devices. 
Furthermore, unlike in previous constructions, the 
present design protects the sensitive semiconductor 
surface from ambients and excludes an air space in the 
device capsule, which expands or contracts with tem- 
perature variations.
particularly desirable as force or pressure sen- 
sors in biomedical applications. 
Details may be obtained from: 
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Price: $3.00 
Reference: TSP68- 10563 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C. 20546. 
Source: W. Rindner, A. Ian nini, and André Garfein

Electronics Research Center 
(ERC- 10087) 
small con- Notes: 
er and the
	
I. The miniature size and small power requirements 
cate mess	 of these niezoiunction devices should make them 
Brief 68-10563	 Category 01


Pressure-sensitive bonded junction transducers

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