An invention relating to the use of a standing acoustic wave charge storage device as an image readout device is described. A frequency f sub 1 was applied to the storage transfer device to create a traveling electric field in the device in one direction along a straight line. A second frequency f sub 2 was applied to the charge transfer device to create a traveling electric field opposite to the first traveling electric field. A standing wave was created. When an image was focused on the charge transfer device, light was stored in the wells of the standing wave. When the frequency f sub 2 is removed from the device, the standing wave tends to break up and the charges stored move to an electrode connected to an output terminal and to a utilization device where the received charges represent the image on the surface of the charge transfer device along a projection of said straight line

Benz, H. A.

English

NASA Technical Reports Server

United States Patent 4,279,001 
Benz [45] Jul. 14, 1981 
IMAGE READOUT DEVICE WITH 
ELECTRONICALLY VARIABLE SPATIAL 
RESOLUTION 
Inventor: 
Assignee: 
Harry A. Benz, Newport News, Va. 
The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
Appl. NO.: 135,039 
Filed: Mar. 28,1980 
Int. ( 3 . 3  ............................................... H04N 5/30 
U.S. Cl. .................................................... 358/213 
Field of Search ................. 358/213, 212; 310/322 
References Cited 
U.S. PATENT DOCUMENTS 
4,053,934 10/1977 Kornreich et al. .................. 358/213 
Primary Examiner-Robert L. Richardson 
Attorney, Agent, or Firm-Howard J. Osborn; John R. 
Manning; William H. King 
1571 ABSTRACT 
This invention relates to the use of a standing acoustic 
wave charge storage device 11 as an image readout 
device. A frequency 4 2 2  is applied to the storage trans- 
fer device to create a traveling electric field in the de- 
vice in one direction along a straight line. A second 
frequency f2 23 which is a harmonic of fl, has the same 
amplitude as 4 ,  and is phase stable with fl  is applied to 
the charge transfer device to create a traveling electric 
field in the opposite-direction to the first traveling elec- 
tric field. Consequently, a standing wave (FIG. 2) is 
created in the charge transfer device along the straight 
line. When an image 25 is focused on the charge transfer 
device, light is stored in the wells of the standing wave. 
Thereafter when the frequency f2 is removed from the 
device, the standing wave tends to break up (FIG. 3) 
and the charges stored therein are moved to an elec- 
trode 18 which is connected to an output terminal 19. 
This terminal is connected to a utilization device 28 
where the received charges represent the image on the 
surface of the charge transfer device along a projection 
of said straight line. 
8 Claims, 4 Drawing Figures 
https://ntrs.nasa.gov/search.jsp?R=19820016540 2020-03-21T16:42:37+00:00Z
U.S. Patent Jui. 14, 1981 Sheet 1 of 2 4,279,001 
U.S. Patent Jui. 14, 1981 
T x- 
Sheet 2 of 2 4,279,001 
I M cu J 
I I 
- 
cu 
I 
‘0 cu 
1 
4,279,001 
2 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a block diagram of the invention with a 
cross-sectional view of the charge t:ansfer device used; 
FIG. 2 is a drawing of the standing wave created in 
the charge transfer device; 
IMAGE READOUT DEVICE WITH 
ELECTRONICALLY VARIABLE SPATIAL 
RESOLUTION 
ORIGIN OF THE INVENTION 
5 
FIG. 3 is a drawing of the standing wave created in 
the charge transfer device immediately after one of the 
signals is removed from the device; and 
view of the charge transfer device. 
The invention described herein was made by an em- 
ployee of the United States Government and may be 
governmental purposes without the payment of any 
rovalties thereon or therefor. 
manufactured and used by Or for the Government for 10 FIG. 4 is a block diagram of the invention with a top 
BACKGROUND OF THE INVENTION DETAILED DESCRIPTION OF THE INVENTION 
The invention relates generally to a surface acoustic 15 Turning now to the embodiment of the invention 
wave (SAW) charge transfer device (CTD) and more selected for illustration in the drawings the number 11 
specifically concerns the use of a surface acoustic wave in FIG, designates a cross-sectiona~ view of a surface 
which the spatial resolution of the readout device can fer device 11 includes a n-type silicon substrate 12, a 
be changed by electronic means. 20 thermally grown silicon dioxide layer 13, and a sput- 
In a surface acoustic wave charge transfer device, tered film 14 of piezoelectric Z n ~ ,  An electrode 15 
surface acoustic waves are used to create traveling which is connected to ground is deposited on the sub- 
longitudinal electric fields in the device. These travel- strate 12, A metallic biasing plate 16 is de- 
ing electric fields create potential wells which will posited on layer 14 and is connected through a variable 
carry charges that may be stored in the The 25 voltage 17 to ground. The presence of the biasing plate 
charges can be injected into the wells by Of light. 16 enhances the acoustoelectric potential at the silicone 
It is the primary Purpose of the invention to use a dioxide interface, thus resulting in a more efficient de- 
surface acoustic wave charge transfer device as an vice. A charge detecting diode 18 is located in layer 12 
image readout device in which the spatial resolution can and connected to a terminal 19. 
be varied by electronic means. The charge transfer device 11 is excited by interdig- 
ita1 transducers 20 and 21 which are placed on the sur- 
face of layer 14. An fi frequency source 22 is applied to 
SUMMARY OF THE INVENTION 
In the present invention several Surface acoustic interdigital transducer 21 which, as is well known, pro- 
wave charge transfer devices are constructed side by duces a traveling electric field along a straight line in 
side 0" a monolitv sdMrate Such that the 35 the silicon substrate 12. An f2 frequency source 23 is 
longitudinal electnc fields created in the substrate are applied to interdigital transducer 21 to produce a set- 
evenly spaced straight lines parallel to each other. Each traveling field opposite to the one produced by 
of the charge transfer devices is fed by signal having a interdigital transducer 20. The frequency f2 is a bar- 
first frequency to Create traveling electrical fields along manic of the frequency fl, has the Same amplitude as the 
the straight lines in one direction. The charge transfer 40 frequency f l  and is phase stable with respect to fl. Con- 
devices are also fed by a signal having a ~ c o n d  fre- sequently, a standing wave such as that shown in FIG. 
quencY such that the resulting traveling longitudinal 2 is produced in substrate 12. The frequency of this 
electrical fields created in the charge transfer devices standing wave is equal to the frequency f l  minus the 
are along the straight lines in the opposite direction. frequency f2. 
The second frequency signal is a harmonic of the first 45 An object 24 is illuminated by a light Source 25 such 
frequency signal, has the Same amplitude as the first that a lens system 26 forms an image of the object on the 
frequency signal, and is phase stable with respect to the surface of charge transfer device 11. This image causes 
first frequency signal. As a result of these traveling charges to be stored in the potential wells of the stand- 
longitudinal electric fields bucking each other along ing wave shown in FIG. 2. Biasing plate 16 provides a 
each of the straight lines, standing waves are formed 5 0  d.c. bias necessary for the nodes of the standing wave to 
which have a frequency equal to the difference in the confine the collected charges. Whenever the frequency 
frequencies of the first and second frequency signals. source 23 is disconnected from the interdigital trans- 
Consequently, when light strikes the device, charges ducer 21 the standing wave tends to break up as shown 
are stored in the wells of the standing waves. Thereaf- in FIG. 3. That is, the standing wave nearest the inter- 
ter, the second frequency signal is removed from the 55 digital transducer 21 breaks up first, then the next one, 
device causing the standing wave to break up and then and so on until the complete standing wave has broken 
the traveling longitudinal electric field caused by the up. As the standing wave is being broken up, the travel- 
first frequency signal tends to push the charges through ing electric field produced by fl pushes the charges 
the device. An electrode for each standing wave is released by the standing wave in the direction of diode 
appropriately located so these charges can be removed 60 18. Hence, after f2 is removed, the packet of charges xi 
from the device and applied to a utilization circuit. The are first applied to the diode 18, then the charges x2 are 
magnitude and time location of each charge are indica- applied to the diode and so forth. It can therefore be 
tive of the intensity of the light and the spatial location readily seen that the charges xi, xi, x3, . . . represent the 
of that intensity. Inasmuch as the second frequency can image along a straight line between interdigital trans- 
be changed and still maintain the required relationship 65 ducers 20 and 21. The standing wave collapses to the 
with the first frequency, the second frequency can be traveling wave from fl at the piezoacoustic velocity of 
changed to thereby change the spatial resolution of the the wave in the medium. A control circuitry 27 discon- 
device. nects the frequency source 23 from the interdigital 
charge transfer device as an image readout device in acoustic wave charge transfer device. The charge trans- 
30 
3 
4,279,001 
transducer 21 and also provides a signal to a utilization 
circuitry 28 to determine the relative times of the signals 
received by the utilization circuitry 28 from electrode 
18. 
FIG. 4 shows the top view of the device in FIG. 1 in 
which several interdigital transducers 20 are driven by 
the single frequency source 22 and several interdigital 
transducers 21 are driven by the single frequency 
source 23. This can be done as long as the channels and 
the detecting diodes are suitably separated. 
The advantage of this invention is that it provides 
means for changing the spatial resolution of an image 
readout device by electronic means. That is, the spatial 
resolution of the output of the device can be controlled 
by changing the frequency of frequency source 23. 
It is to be understood that the form of the invention 
herewith shown and described is to be taken as a pre- 
ferred embodiment. Various changes may be made in 
the device without departing from the invention. For 
example, changes in frequency at either side will change 
the spatial resolution of the standing wave and therefore 
the equivalent detector resolution as long as the ampli- 
tude and phase reqirements of the acoustic waves are 
maintained. Also, the structure could easily extend to 
the second dimension by using an additional pair of 
surface acoustic wave structures in the y-direction, also 
driven at harmonically related frequencies in matching 
amplitudes to define the standing wave in the y-direc- 
tion, which will effectively separate the x-direction 
channels in much the same way as the barrier diodes or 
overlaying geometry. Similarly, a y-direction resolution 
variation with clocking could be achieved by changing 
the harmonic relation between the traveling waves. 
Thus by changing in driving in a dynamic way the 
resolution of the sensor in both directions could be 
changed by clocking only. 
What is claimed is: 
1. In an image readout device, a detector for detect- 
ing light at discrete points along a straight line compris- 
ing: 
a surface acoustic wave charge transfer device which 
in response to a frequency source produces a trav- 
eling longitudinal electric field in the device that 
creates potential wells which carry charges that 
are injected into the wells by light that strikes the 
device; 
a first means for applying a frequency fl  to said 
charge transfer device for producing a first travel- 
ing longitudinal electric field in the device along 
said straight line; 
a second means for applying a frequency f2 to said 
charge transfer device for producing a second trav- 
eling longitudinal electric field in the device along 
said straight line in the direction opposite to the 
electric field produced by said first means; 
wherein f2 is a harmonic of fl, has the same amplitude 
as fl  and is phase stable with f1, whereby the first 
and second traveling longitudinal fields produce a 
standing wave along said straight line that has a 
frequency equal to the difference of fl  and f2; 
means for applying an image to said device whereby 
5 
10 
I5 
20 
25 
30 
35 
40 
45 
50 
55 
60 
.. - 
light charges are stored in the wells of said standing 
wave; 
means for disconnecting f2 from said device whereby 65 
said standing wave breaks up and the charges 
stored in the wells of said standing wave are moved 
4 
along said straight line by the first traveling longi- 
tudinal electric field; and 
electrode means included with said charge transfer 
device receiving the charges moved along said 
straight line by the first traveling longitudinal elec- 
tric field. 
2. In an image readout device, a detector according to 
claim 1 wherein said acoustic wave charge transfer 
device comprises an n-type semiconductor substrate; an 
insulating layer and a piezoelectric layer. 
3. In an image readout device, a detector according to 
claim 2 including an electrode on the side of said sub- 
strate opposite said silicon dioxide layer, a conductive 
transparent bias plate on the film of piezoelectric ZnO 
and means for applying a voltage to the bias plate. 
4. In an image readout device, a detector according to 
claim 1 including means for varying the frequency of f2 
whereby the spatial resolution of the charges received 
by said electrode means is varied. 
5. In an image readout device, a detector according to 
claim 1 including circuit means connected to said elec- 
trode means for utilizing the resulting multiplexed sig- 
nals at the electrode means. 
6. An image readout device comprising: 
a surface acoustic wave charge transfer device which 
in response to a frequency source produces a trav- 
eling longitudinal electric field in the device that 
creates potential wells which carry charges that 
are injected into the wells by light that strikes the 
device; 
a first means for appylying a frequency f1 to said 
charge transfer device at n different locations for 
producing n first traveling longitudinal electric 
fields in the device along n straight lines that are 
parallel to each other; 
a second means for applying a frequency f2 to said 
charge transfer device at n different locations for 
producing n second traveling longitudinal electric 
fields in the device along said n straight lines in the 
direction opposite to the electric fields produced 
by said first means; 
wherein f2 is a harmonic of fi, has the same amplitude 
as f l  and is phase stable with fl, whereby the first 
and second traveling longitudinal fields produce n 
standing waves along said n straight lines that have 
a frequency equal to the difference of fl  and f2; 
means for applying an image to said device whereby 
light charges are stored in the wells of said standing 
waves; 
means for disconnecting f2 from said device whereby 
said standing waves break up and the charges 
stored in the wells of said standing waves are 
moved along said straight lines by the first travel- 
ing longitudinal electric fields; and 
n electrode means included with said charge transfer 
device for receiving the charges moved along said 
n straight lines by the first traveling longitudinal 
electric fields. 
7. An image readout device according to claim 6 
wherein said acoustic wave charge transfer device com- 
prises an n-type semiconductor substrate, an insulating 
layer and a piezoelectric layer. 
8. An image readout device according to claim 7 
including circuit means connected to said n electrode 
means for utilizing the resulting multiplexed signals at 
the n electrode means. * * * * *  


Image readout device with electronically variable spatial resolution

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server