Two techniques have been conceptually proposed as possible means of reducing parasitic beta in lateral p-n-p transistors. One method uses a degenerate substrate and high concentration P /plus/ guard-ring diffusion, another places the base contact at the center of an annular ring structure

Gallagher, R. C.

Scott, J. M.

English

NASA Technical Reports Server

July 1969	 Brief 69-10244 
NASA TECH BRIEF	
A, All 
- 
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. 
Conceptual Techniques for Reducing Parasitic Current Gain

of Lateral PNP Transistors 
.
Base	 Emitter	 Collector N+ 
P-	 T2 Ti	 P P+ Floating N+ Diffusion 
Ti>> T2 
Fig. 1. Isolation Diffused Lateral PNP Structure 
Two proposed techniques are presented as possible 
means of reducing parasitic Beta in lateral PNP 
transistors. These methods may be applicable and of 
interest to persons and organizations involved in the 
fabrication, design, and development of semiconductor 
components and integrated circuits. 
The problem: 
Lateral PNP bipolar transistors require isolation of 
the "active" regions of the device structure from the 
- substrate and peripheral boundaries in order to reduce 
parasitic Beta. Conventional fabrication process tech-
niques require additional photoresist and diffusion 
steps to accomplish this. 
The solution: 
Two methods have been conceptually proposed to 
provide the isolation. 
Method (I) uses a degenerate substrate and a high 
concentration p guard-ring diffusion. 
Method (2) places the base contact at the center of 
an annular ring structure to improve lateral PNP 
transistor action and reduce parasitic Beta. 
How it's done: 
Method (I). The diffusion used for the isolation of
Emitter 
Collector	 Base 
W 1 =W2 =W3 =W4 = Base width 
Fig. 2. Annular Ring PNP Structure 
the epitaxy region is also used to form the emitter and 
collector regions. A cross-sectional view of the device 
shown in Figure 1 demonstrates the stopping action 
of the floating N diffusion located beneath the 
emitter and collector. The lifetime, r 2 , of the N 
region is much lower than r 1 of the epitaxy base. The 
isolation diffusion guard-ring has a surface concentra-
tion between 5.0 x l0' - 5.0 x 1020 which is suffi-
cient to maintain the injection efficiency. 
Method (2). The base contact on a lateral PNP de-
vice is normally located on the outside of the collector 
region. If the base contact is located within the emitter, 
the emitter will assume a donut shape rather than a 
circular shape. Since the emitter injects from both 
sides, the collector should completely encircle the 
emitter. The annular ring structure shown in Figure 2 
accomplishes this and also maximizes the emitter in-
jection efficiency for a given area. This structure gives 
a base contact that is symmetrical to the structure 
rather than a non-symmetric location outside the col- 
lector and provides for collection of minority carriers 
injected towards the center as well as those which are 
injected radially. (continued ocerleal) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19690000244 2020-03-16T17:45:07+00:00Z
Notes:	 Patent status: 
I. No further documentation is available. 	 No patent action is contemplated by NASA. 
2. Inquiries may be directed to:	 Source: R. C. Gallagher and J. M. Scott of 
Technology Utilization Officer	 Westinghouse Electric Corporation 
Manned Spacecraft Center 	 under contract to 
Houston, Texas 77058 	 Manned Spacecraft Center 
Reference: B69-10244
	
	
(MSC-13200)
(MSC-13 199) 
I
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Brief 69-10244	 Category 01


Conceptual techniques for reducing parasitic current gain of lateral pnp transistors

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