To measure vacuum pressures in the range of 5 times 10 to the minus 7 to 5 times 10 to the minus 16, a semiconductor resistor composed of sintered zinc oxide is used. Through the effect of surface absorbed gases on the resistance of the semiconductor material, very low pressures are measured

Medved, D. B.

English

NASA Technical Reports Server

September 1969	 Brief 69-10421 
NASA TECH BRIEF 
NASA Teèh 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. 
------	
-__j_ 
Concept for Improved Vacuum Pressure Measuring Device 
Vacuum System to be 
Monitored
Optical Port
Electrical Feed-Throughs 
Semiconductor Element 
"Standard Light Source 
Schematic Drawing For Low Pressure Measuring Concept 
	
This concept for measuring vacuum pressures in
	 measuring low vacuum pressures below 10-14 torr. 
	
the range from 5 x 10 to 5 x 10- 16 torr should	 Above this pressure range, the standard procedure 
	
prove of interest to research and development
	 has been to employ some form of electron bombard-
	
manufacturers of vacuum tube and related measur-
	 ment-ionization system. 
	
ing devices. The basic element upon which the meas-
	 In measuring very low pressures, the development 
	
uring concept depends is a semiconductor resistor,
	 of sensing elements uniquely sensitive to specific 
	
composed of sintered zinc oxide. Through the effect
	 gas species has been an important area of research. 
	
of surface adsorbed gases on the resistance of semi--
	 The key- element should have a large surface to vol-
	
conductor materials, very low pressures can be
	 ume ratio, and the carrier concentration of electrons 
	
measured. No existing techniques are capable of
	 in the bulk which dominates the resistance charac-
(continued overleaf) 
	
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 
	
Government nor any person acting on behalf of the United States	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19690000413 2020-03-16T18:16:04+00:00Z
teristics of the specimen should be highly sensitive 
to the surface adsorption of the species to be meas-
ured. 
There are several methods which-can be used to 
measure very low pressures. One approach is to 
monitor the resistance of the semiconductor element 
as a function of time under the vacuum conditions 
to be monitored before, during, and after illumination 
to visible light of moderate ,
 intensities. This light 
source can be inside or outside of the vacuum system. 
An alternate method is to substitute the standard 
light source inside the vacuum system with a simple 
filament placed in a pertinent geometrical relation-
ship to the resistance element. This light source cleans 
the semiconductor surfaces by specific mechanisms. 
The decay or increase in the resistance following the 
cleaning procedure is then monitored by the resist-
ance bridge. By means of appropriate calibration, a 
direct reading of the vacuum conditions can be 
obtained. 
Another procedure substitutes heat for photon 
light and cleans the resistance element with temp-
eratures in the vicinity of 400°C. This can be achieved 
by a filament placed near the filament. A heat sink 
contact and standard flashing techniques can also 
be employed. 
Notes: 
For further information on the theory of this con-
cept, see: 
I. J. of Chemical Physics, vol. 28, # 5 , May 1958, pp. 
870-873. 
2. J. of Physics and Chemistry of Solids, vol. 20, #3/ 
#4, pp. 255-267. Published in Great Britain. 
3. This development is in a conceptual stage only, 
and as of date of publication of this Tech Brief, 
neither a model nor prototype has been constructed. 
4. No further documentation is available. 
Patent status: 
No paten t action is contemplated by NASA. 
Source: D.B. Medved of 
Electro-Optical Systems, inc. 
under contract to 
Marshall Space Flight Center 
(M FS-20 172)
S 
Brief 69-10421	
.
	 Category 02


Concept for improved vacuum pressure measuring device

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server