Gamma, X-ray, electron, or other radiation is used to shift threshold potentials of MOS devices on logic circuits. Before irradiation MOS gates to be shifted are biased positive and other gates are grounded to substrate. Threshold lasts 10 years. Thermal annealing brings circuit back to original configuration

Danchenko, V.

Schaefer, D. H.

English

NASA Technical Reports Server

December 1972
	 B72-10719 
•
	
NASA TECH BRIEF 
Goddard Space Flight Center 
NASA Tech Briefs announce now technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Irradiation of MOS—FET Devices to Provide

Desired Logic Functions 
0
The problem: 
A common device used in read-only memories is the 
MOS-FET (metal-oxide semiconductor field-effect tran-
sistor). For a given logic function, these devices are 
arranged in a specific configuration on the surface of 
a single silicon strip. The development of each con-
figuration is costly, and, once fabricated, the circuit 
is limited to a single logic function because of fixed 
thresholds of each MOS. 
The solution: 
Selective irradiation can be effectively used to re-
design the MOS logic circuits. 
How it's done: 
This method employs radiation such as gamma, 
X-rays, electrons, etc. to shift the threshold potentials 
of selected MOS devices on the logic circuits. Before 
irradiation, the gates of selected MOS must be biased 
positive, while gates of devices whose thresholds are 
not to be shifted are grounded to the substrate. The 
irradiation is then easily accomplished in a few minutes. 
To verify this method, two p-channel MOS devices 
each having a -3.7V threshold were irradiated with a 
total dose of 3 x 10 12 e/CM2. One device was biased 
and the other grounded. As a result of irradiation, the 
biased device threshold shifted to 18.7V, while that 
of the unbiased only shifted to 5.8V. Thus, if the 
-10V gate potential were applied to both devices, only 
the latter would turn on, whereas, before irradiation, 
both would have turned on.
It is estimated that irradiation will maintain the 
device threshold for ten years. The circuit can be 
brought back at any time to its original configuration 
by the thermal annealing of radiation effects. 
In the case of n-channel MOS devices, radiation with 
bias can induce channel conduction even with zero 
gate voltage. 
The obvious advantage of this capability is thatMOS 
circuits designed for a specific logic function can be 
easily converted to perform a different logic. 
Notes: 
1. Prior to application of this concept the following 
information is required: 
(a) The relationship between radiation energy, total 
dose, and change in threshold voltage. 
(b) Verification of the necessity for maximum 
irradiation to the point of saturation to obtain 
stability. 
(c) The decay rate versus temperature relationship. 
2. Requests for further information may be directed to: 
Technology Utilization Officer 
Goddard Space Flight Center 
Code 207.1 
Greenbelt, Maryland 20771 
Reference: TSP72-10719 
Patent status: 
NASA has decided not to apply for a patent. 
Source: V. Danchenko and D.H. Schaefer

Goddard Space Flight Center

(GSC-1 1061) 
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Government nor any person acting on behalf of the United States
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Irradiation of MOS-FET devices to provide desired logic functions

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