Information
-
Patent Grant
-
6396253
-
Patent Number
6,396,253
-
Date Filed
Friday, November 19, 199924 years ago
-
Date Issued
Tuesday, May 28, 200222 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Metjahic; Safet
- Hamdan; Wasseem H.
Agents
- Horton, Esq.; Carl B.
- Armstrong Teasdale LLP
-
CPC
-
US Classifications
Field of Search
US
- 324 731
- 324 1581
- 324 711
- 324 522
- 324 523
- 324 527
- 378 207
- 382 309
- 349 55
-
International Classifications
- G01R3102
- G01R3108
- G01R104
- G01N2700
-
Abstract
A method for detecting cut data lines in an imaging array having a detector including an array of pixels for measuring radiation, and a plurality of data line contacts is provided. The method includes the steps of initializing pixels of the imaging array which includes a plurality of data lines including at least one uncut data line and at least one cut data line, wherein each cut data line is electrically connected to at least one of the plurality of data line contacts and at least one uncommitted contact. The method further includes determining a signal level for the uncut data lines, measuring a signal level of each data line in the plurality of data lines, and determining a number of cut data lines and a number of uncut data lines by using the signal levels received from each data line in the plurality of data.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to radiation imager arrays and more specifically to automated methods and apparatus for the repairs of such arrays.
Complex electronic devices are commonly formed on substrates in fabrication processes involving deposition and patterning of multiple layers of s conductive, semiconductive, and dielectric materials to form multiple individual electronic components. For example, large area imager arrays are fabricated on a wafer. These arrays contain photodiodes and circuitry for reading the output of the photodiodes. The circuitry includes scan (address) lines, data lines and switching components (e.g., field effect transistors (FETs)). In such an array, both scan and data lines are contacted using separate sets of contacts on the panel. Additionally, half of the drive electronics are connected to a set of contacts on the outer edge of the panel which connect to “odd” scan lines. Between these contacts and an active area of the panel are another set of contacts which connect to “even” scan lines. Sense electronics are on the remaining two sides of the panel. One set of sense electronics connects to all “odd” data lines on one side of the panel and the other set of sense electronics connects to “even” data lines on the opposite side. None of the scan or data lines are contacted on both sides of the panel.
Defects in such imager arrays can result from, among other causes, impurities in materials deposited to form the various components. One example of such an impurity-based defect is a short circuit between a data line and an underlying scan (address) line in the pixel array. Such short circuits disrupt the desired electrical connections between devices in the array and seriously degrade performance of one or more individual electronic components on the wafer, often to the point of making an entire wafer unusable. In order to improve the yield of flat panel X-Ray detectors, shorts between a scan line and a data line, which would normally result in both the data line and the scan line being unusable, are removed in a fashion that allows both the scan and the data line to be recovered with only a small number of pixels being lost in an immediate vicinity of the short. Generally two cuts are made on either side of the short on the line which can be most easily recovered (or “repaired”).
Repair and recovery of data lines that have been cut on flat panel x-ray panels are made possible by addition of a small number of uncommitted contacts.
Uncommitted contacts are connected to a “free” end of a data line that has been cut in two places to remove a short. A free end of a data line in this instance refers to a cut end of a data line that is no longer attached to sense electronics on an opposite side because of the cut. Without recovery, data on this free end would normally be lost, representing loss of at least a partial (data) line for every short removed by cutting.
Uncommitted contacts on the opposite end can be used to short to the free end of a cut data line. In effect, a free end of an “odd” cut data line becomes a partial “even” data line by connection to an uncommitted contact on the end opposite where the “odd” sense electronics.
The uncommitted contacts are not connected to any data lines during fabrication, but are designed to allow a short between a free end of a cut data line and an uncommitted contact to be made easily on the panel. When a data line has been cut and is connected to an uncommitted contact, data from the free end of the cut data line will be displaced spatially in the resulting acquired image. Because this image is represented as an array of binary numbers in computer memory, displaced data can be re-mapped to its correct location in the image presented for diagnosis using simple computer-based replacement algorithms. A part of this process particular to each panel is a set of locations at which cuts have been made and which uncommitted contacts have been used to recover cut data lines. It has been suggested that during the process of test and repair, a file be created to record both locations of cuts and locations of uncommitted contacts which have been used to recover cut data lines.
This file would have to accompany the panel to a system that uses this panel to generate diagnostic quality x-ray images, to enable the system to reconstruct an image from the repaired panel. This data would be different for every panel.
Successfully transferring remapping information to end users can be difficult due to logistics. Loss of data in a remapping information file can occur for various reasons, for example, corruption of data in the file itself, or loss or destruction of the media. If the file is not successfully transferred, the file must be regenerated, or else the detector assembly may become useless scrap. It would therefore be desirable to provide methods and apparatus that would make transfer of remapping information files to end users unnecessary. It would also be desirable to automate this remapping at a site of an end user.
BRIEF SUMMARY OF THE INVENTION
A method is disclosed for detecting repairs made and data lines cut in an imaging array which includes an array of pixels for measuring radiation, and a plurality of data lines for reading data from the pixels, and a number of uncommitted data line contacts to be used for repairing shorted data lines. The method includes the steps of initializing the pixels of the imaging array, determining a signal level for the data lines that have not been cut, measuring a signal level of each data line in the array, and determining if the signal level for each data line is equivalent to the uncut data line signal level.
The above described method eliminates the need for shipping remapping information files with repaired detectors. In addition, the possibility that the media containing the remapping information file is compromised during shipping of the imaging array is eliminated.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a cross-sectional view of a portion of an imager assembly having an undesired conductive path between a data line and a scan line in the array;
FIG. 2
is a plan view of a photosensor array having scan lines and data lines with a plurality of electrical contact pads along its edges;
FIG. 3
is a plan view of a photosensor array showing one scan line and one data line that has been repaired with the free end of the data line connected to an uncommitted contact; and
FIG. 4
is a schematic view of a photosensor array having scan lines, data lines, photodiodes and thin film transistors.
DETAILED DESCRIPTION OF THE INVENTION
In one embodiment and referring to
FIG. 1
, a radiation imager assembly
10
, for example, an x-ray imager, typically comprises a substrate
12
on which a pixel array, sometimes called a photosensor array
14
is disposed. Photosensor array
14
includes a plurality of electronic components, such as scan lines
16
, photodiodes
18
, and switching devices including field effect transistors (FETs) (not shown in FIG.
1
). FETs are disposed to selectively couple respective photodiodes
18
to selected data lines
20
. Imager assembly
10
is an x- y- addressed imager. More specifically, a plurality of scan lines
16
for addressing individual pixels (not shown) in photosensor array
14
includes a plurality of data lines
20
(FIG.
2
), and a plurality of scan lines
16
. Each data line
20
is oriented substantially along a first axis of imager assembly
10
, and each scan line
16
is oriented substantially along a second axis of imager assembly
10
. The first and second axes of imager assembly
10
are disposed substantially perpendicular to one another. For ease of illustration in
FIG. 2
, only a few of data lines
20
and scan lines
16
are shown extending across photosensor array
14
, although each set of scan lines
16
extend across photosensor array
14
. Scan lines
16
and data lines
20
are arranged in rows and columns so that single pixels in photosensor array
14
are addressable by one scan line
16
and one data line
20
. Scan lines
16
comprise a conductive material, such as molybdenum, aluminum, or the like. Photodiodes
18
(not shown in
FIG. 2
) are electrically coupled to data lines
20
via the FETs (not shown in FIG.
2
). Only a portion of each photodiode
18
is illustrated in the particular cross section of
FIG. 1
; photodiodes
18
comprise the active portion of the array that is responsive to incident photons and that produces the electric signals corresponding to the detected incident light. X-ray energy is converted to light energy by passing through a layer of phosphor (not shown), such as cesium iodide which is normally disposed near the surface of photodiodes
18
. Each photodiode
18
comprises a layer of intrinsic amorphous silicon disposed between a layer of silicon doped to exhibit p type conductivity and a layer of silicon doped to exhibit n type conductivity.
A representative short circuit condition is illustrated in
FIGS. 1 and 2
. The short circuit condition results from, for example, a defect
22
in dielectric material
24
that comprises an impurity in the dielectric material
24
. Typically an electrically conductive material that became entrained with deposited dielectric material
24
as it was deposited, or as an artifact from the deposition of other components in the photosensor array
14
. As illustrated in
FIGS. 1 and 2
, defect
22
is disposed such that it is electrically coupled to data line
20
and to scan line
16
such that a conductive path between scan line
16
and data line
20
exists. Such a conductive path is undesired as it shorts two conductive layers together, degrading the signal generated by pixels coupled to that data line
20
and scan line
16
. Until such time as the short to affected scan line
16
is isolated, operation of the whole photosensor array
14
is degraded. Uncompromised data lines
26
are shown for illustration purposes.
A “repaired” portion of a photosensor array
30
with a “repaired” data line
32
is illustrated in FIG.
3
. Cuts
34
are on each side of defect
36
. A “free” end of cut data line
38
is electrically connected to an uncommitted contact
40
. Shortened data line
42
is connected to its respective contact
44
as always. Drive circuits
46
are connected to scan lines
16
(shown in
FIG. 2
) and enable photosensor array
30
, allowing read circuits
48
to read the data present on data lines
20
(shown in FIG.
2
).
Referring to
FIG. 4
, data lines
20
(also shown in
FIG. 1 and 2
) that have been cut are detected, in one embodiment, by an artifact prevalent in amorphous silicon FETs
50
known as charge retention. Scanning a dark (or offset) image in the absence of X-Ray and light (i.e. a dark scan) results in a signal that is slightly negative. This negative charge is “retained” by the FET
50
in the panel from when it is turned on, or scanned. Retained charge leaks out slowly over time and adds a positive signal to pixels that are read or scanned later in time. The net effect is a slightly negative offset. When a data line
20
is cut, sense electronics register no offset. Therefore a sense electronics channel connected to an uncommitted contact
40
(shown in
FIG. 3
) or shortened data line
42
(shown in
FIG. 3
) reports a slightly higher signal level, than a channel connected to an uncompromised data line
26
(shown in FIG.
2
). A “natural” offset of each channel is determined by keeping FETs
50
on the panel off and acquiring an image. When FETs
50
are turned on by drive circuits
46
(shown in
FIG. 3
) during the acquisition of a dark image, those channels that are connected to an uncompromised data line
26
will report a slightly lower signal level to read circuits
48
(shown in
FIG. 3
) in a dark image than in a “FET off” image. Gain and conversion parameters are selected to accentuate a difference between connected and unconnected data lines. Shortened data lines
42
(shown in
FIG. 3
) can be determined by examining data along the data lines
20
using read circuits
48
. If a step in signal level exists as data along each data line
20
is examined, then it is deduced that a cut
34
(shown in
FIG. 3
) has been made in that data line. A portion of the data line
20
that has a higher average signal level is a cut portion from a sense electronic channel that normally services the cut data line. Channels that are connected to normally uncommitted contacts
40
(shown in
FIG. 3
) are examined in a similar manner. Because only “local” uncommitted contacts
40
are used for recovery, only a small number of channels need to be examined for a step complementary to one discovered in a cut data line.
In one embodiment uncommitted contact channels are examined first, so that an exact number of cuts in a group, which is a subset of the radiation imager assembly
10
, can be determined without having to examine every line in the group.
As illustrated in
FIG. 3
, an uncommitted contact
40
is electrically connected to a free end of cut data line
38
. If no uncommitted contacts
40
for a group appears to have “image” data present, i.e. a lower offset value, that group is skipped entirely. Similarly, when a match for each used uncommitted contact
40
(now repair) channel is found in a group, matching for that group is complete, even if all data lines in that group have not been examined. Data from a “lower” average value portion of the uncommitted contact channel is used to replace data in a “higher” average value portion of cut data line. A repaired data line
32
(shown in
FIG. 3
) is correlated with great certainty to an uncommitted contact
40
by a position of a “step” in data along the uncommitted contact
40
channel used for repair.
In one embodiment, a rule defining an ordering in which shorts between repaired data lines
32
and uncommitted contacts
40
are made is applied during a recovery portion of test and repair. Application of this rule makes it possible to determine, with certainty, associations between cut data lines and uncommitted contact channels when two even (or two odd) data lines belonging to a single pattern are cut at the same scan line
16
(shown in
FIGS. 1
,
2
, and
3
).
In another embodiment, rather than using retained charge to determine connectivity, a parasitic capacitance that exists between each scan line and every data line is used to induce a signal level on sense electronics by stretching a period that the FET is turned on past a time when the sense electronics takes its sample. An effect resulting from parasitic capacitance is large enough to drive the sense electronics much more negative than a nominal charge retention effect. Channels connected to data lines (or portions thereof) appear as black lines. As a result, channels not connected to data lines return a nominal “natural” offset, or signal level of that channel of the sense electronics.
From the preceding description of various embodiments of the present invention, it is evident that the need for shipping remapping information files with a repaired detector is eliminated. In addition, detectors are independent of the imaging systems since the repair file no longer needs to accompany a detector if it is not always to be connected to the same system for its entire useful life.
Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is intended by way of illustration and example only and is not to be taken by way of limitation. Accordingly, the spirit and scope of the invention are to be limited only by the terms of the appended claims and their equivalents.
Claims
- 1. A method for detecting cut data lines in an imaging array having a detector including an array of pixels for measuring radiation and a plurality of data line contacts, said method comprising the steps of:initializing pixels of the imaging array which includes a plurality of data lines including at least one uncut data line and at least one cut data line, wherein each cut data line is electrically connected to at least one of the plurality of data line contacts and at least one uncommitted contact; determining a signal level for the uncut data line; measuring a signal level of each data line in the plurality of data lines; and determining if the signal level received from each data line in the plurality of data lines is equivalent to the uncut data line signal level.
- 2. A method according to claim 1 wherein said step of initializing the pixels of the imaging array comprises the step of performing a dark scan.
- 3. A method according to claim 1 further comprising the step of determining a signal level at each data line contact due to an amount of charge retained by a field effect transistor in the pixel array in the initialization of the pixel array.
- 4. A method according to claim 1 further comprising the step of determining a signal level at each data line contact due to parasitic capacitance between each data line and a scan line of the pixel array and induced by stretching a period that a FET is turned on past a time when a sense electronics takes a sample.
- 5. A method according to claim 1 further comprising the step of determining a number of cut data lines.
- 6. A method according to claim 5 wherein said step of determining a number of cut data lines comprises the step of subtracting, from the total number of data lines, a number of data lines having a signal level for uncut data lines.
- 7. A method according to claim 5 further comprising the step of applying a previously defined rule defining an order in which uncommitted contacts are used in a recovery portion of test and repair.
- 8. A method according to claim 1 further comprising the step of selecting gain and conversion parameters selected to accentuate a difference in signal levels measured at data line contacts for cut and uncut data lines.
- 9. A method of determining the number of cut data lines in an imaging array, the imaging array having a detector including an array of pixels for measuring radiation and a plurality of data line contacts, said method comprising the steps of:initializing pixels of the imaging array which includes a plurality of data lines including at least one uncut data line and at least one cut data line, wherein each cut data line is electrically connected to at least one of the plurality of data line contacts and at least one uncommitted contact; determining a signal level for the at least one cut data line; measuring a signal level of each uncommitted contact; determining if a number of uncommitted contacts have a signal level equivalent to the cut data line signal level of the at least one cut data line; and subtracting the number of uncommitted contacts having a signal level equivalent to the at least one uncut data line signal level from a total number of uncommitted contacts.
- 10. A method according to claim 9 wherein said step of initializing the pixels of the imaging array comprises the step of performing a dark scan.
- 11. A method according to claim 10 further comprising the step of determining a signal level at each data line contact based on an amount of charge retained by a field effect transistor in the imaging array in the initialization of the pixel array.
- 12. A method according to claim 10 further comprising the step of determining a signal level at each data line contact due to parasitic capacitance between each data line and scan line of the pixel array and induced by stretching a period that the FET is turned on past a time when the sense electronics takes its sample when the scan line is actuated.
- 13. A method according to claim 9 further comprising the step of selecting gain and conversion parameters to accentuate the difference between uncut data lines and unused uncommitted contacts.
- 14. A method according to claim 13 further comprising the step of applying a rule defining an order in which the uncommitted contacts are used in a recovery portion of test and repair.
- 15. An imaging system for generating an image of an object, said imaging system comprising an imaging array comprising an array of pixels for measuring radiation, said imaging system adapted to detect cut data lines in said imaging array by being configured to:initialize the pixels of the array which includes a first set of data lines including at least one of a second set of uncut data lines and a third set of cut data lines, the first set of data lines for reading data from the pixels, a plurality of data line contacts, each data line contact electrically connected to one of the data lines, a plurality of uncommitted contacts, and at least one uncommitted contact connected electrically to one of the cut data lines; determine a signal level for the second set of uncut data lines; measure a signal level of each data line in the first set of data lines; and determine if the signal level for each data line in the first set of data lines is equivalent to the uncut data line signal level.
- 16. An imaging system according to claim 15 further configured to initialize the pixels of the array by performing a dark scan.
- 17. An imaging system according to claim 15 further configured to determine a number of cut data lines.
- 18. An imaging system according to claim 17 further configured to determine a number of cut data lines by subtracting the number of data lines in the second set from the number of data lines in the first set.
- 19. An imaging system according to claim 15 further configured to determine a signal level at each data line contact where the signal level is based on an amount of charge retained by a field effect transistor in the pixel array in the initialization of the pixel array.
- 20. An imaging system according to claim 19 further configured with gain and conversion parameters selected to accentuate a difference in signal levels measured at data line contacts for cut and uncut data lines.
- 21. An imaging system according to claim 15 further configured to determining a signal level at each data line contact due to parasitic capacitance between each data line and scan line of the pixel array and induced by stretching a period that the FET is turned on past a time when the sense electronics takes its sample when the scan line is actuated.
- 22. An imaging system according to claim 15 further configured to subtract the number of uncommitted contacts with a signal level not equivalent to the signal level of the second set of uncut data lines from a total number of uncommitted contacts.
- 23. An imaging system according to claim 15 further configured to move spatially displaced image data collected from cut data lines connected to uncommitted contacts to a correct location in the image.
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