Coil structures have been designed to permit nondestructive testing of bubble wafers. Wafers can be electrically or optically inspected and operated from quasi-static frequency to maximum device operating frequency

Chen, T. T.

Williams, J. L.

English

NASA Technical Reports Server

September 1975	 B75-10197 
NASA TECH BRIEF 
Langley Research Center 
NASA Tech Brefs announce new 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 relatinglo the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Bubble-Domain Circuit Wafer Evaluation Coil Set 
The evaluation of bubble-domain device wafers 
prior to dice operation is necessary to minimize garnet 
(bubble-domain substrate) waste and to select and 
identify good chips. Coil structures have been 
designed to fulfill all the requirements of bubble wafer 
inspection. With them, the wafers can be either 
electrically or optically accessed and operated from 
quasi-static frequency to maximum device operating 
frequency. 
Figure 1 shows a new in-plane field coil winding. 
Two orthogonal flat coils are wound around a 
ferromagnetic plate for supplying a rotating field 
parallel to the ferrite plate in the space above the coil 
winding. The ferrite plate isolates the top (A) and 
bottom (B) windings so that when a garnet device (C) 
is placed on top of the coil, it will "see" a magnetic 
field generated from a layer of. parallel conductor 
currents. The in-plane field, above the center of the 
winding, is uniformly parallel to the ferrite plane and 
has no vertical component. The size of this uniform 
field area depends on the size of the coil winding and 
the distance to the coil winding. 
X-Axis	 -
To achieve a minimum vertical component of the 
in-plane field, two ferrite coils are arranged as top and 
bottom coils with a space between. The current 
•directions in the coils are arranged so that the 
in-plane field components aid each other and the 
vertical components cancel each other in the space 
between the coils. 
The required bias field can be supplied by a regular 
flat circular coil. Figure 2 shows the arrangement 
where the in-plane coil windings enclose both the bias 
field coil (Z-axis winding) and the ferromagnetic 
shielding plate. The wafer sample to be inspected can 
be placed directly on top of this coil structure. The 
sample is readily available to the electrical probe. The 
magnetic domain motion can also be observed by 
using a reflected polarized-light microscope. 
For a high-frequency arrangement, the bias coil is 
mounted outside the in-plane coil so that the in-plane 
coil size will not be limited by the bias coil. A small 
winding on a piece of high-frequency ferrite plate. 
enables the coil to be driven to very high frequency. 
inding
Test 
C
	
Water	 XAxis 
Winding 
Ferromagnetic 
V-Axis	 Plate 
Winding 
Figure 1. In-Plane Field Coil Winding
(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=19750000197 2020-03-19T20:27:42+00:00Z
xis 
ling 
tgnetic 
Plate 
Nonmagnetic  
Wafer Probes
Nonmagnetic 
Substrate 
Z-Axis 
Winding
Figure 2. In-Plane Coil Windings Enclosing Both 
Bias Field Coil and Shielding Plate 
The garnet wafer can be inserted freely and without 
limitation between the in-plane and bias coils. The 
electrical testing probes can be either inserted through 
the center hole of the bias coil or attached under the 
coil and connected from the side. For visual 
observation, microscope objectives can be inserted 
through the center hole of the bias coil. 
Another design provides more accurate measure-
ment of device characteristics, such as operating 
margin. The rotating field is supplied by two ferrite 
coils, and the bias field is generated from a flat coil 
pair. A wafer and wafer probes are inserted between 
the coil pair. It is still an open structure as the top 
coils are removed for probe alinement and visual 
inspection. Since there is minimum vertical bias 
modulation due to in-plane rotating fields, the ferrite 
coil size can be substantially reduced so that it can be 
easily driven to very high frequency.
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
Langley Research Center 
Mail Stop 139-A 
Hampton, Virginia 23665 
Reference: B75-10197 
Patent status: 
Title to this invention has been waived under the 
provisions of the National Aeronautics and Space Act 
[42 U.S.C. 2457W], to the Rockwell International 
Corporation, Anaheim, California 92803. 
Source: Thomas T. Chen and

Jeffrey L. Williams of

Rockwell International Corp.

(LAR-11728) 
Categories: 01 (Electronics - Components 
and Circuitry) 
02 (Electronics Systems) 
03 (Physical Sciences) 
B75-10197
	 04 (Materials)


Bubble-domain circuit wafer evaluation coil set

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