Active solid-state devices (e.g. – transistors – solid-state diode – Test or calibration structure
Reexamination Certificate
2001-08-29
2003-04-22
Niebling, John F. (Department: 2812)
Active solid-state devices (e.g., transistors, solid-state diode
Test or calibration structure
C438S017000
Reexamination Certificate
active
06552359
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a drive circuit for driving a plurality of elements to be driven which is furnished with a test circuit for testing itself. The invention also relates to a method of testing the drive circuit.
To fabricate the recording head of a thermal ink-jet printer, for instance, a drive circuit is formed on a semiconductor substrate (silicon substrate) and overlaid on it with a heater (heat-generating resistor) material, followed by the formation of cavities and orifice nozzles on the heater. The cavities serve as pixel-based ink chambers and ink is projected through the orifice nozzles. Since the ink will be supplied from a back side of the silicon substrate, ink supply holes are made through the silicon substrate.
The heater material is usually polysilicon and other materials that are manufactured in the ordinary semiconductor fabrication process. Occasionally, for instance, Ta alloys and other special materials that are not very common in the ordinary semiconductor fabrication process are employed. In a case of using a special material on the heater, a semiconductor fabrication process for forming the drive circuit is followed by another fabrication process that is intended to form a heater using the Ta alloy.
After the semiconductor fabrication process, it is preferable that the semiconductor device can be tested to confirm its completion without connecting the heater as elements to be driven. If the semiconductor device is found inoperable at this stage, for instance, one can avoid waste by not forming a heater on a defective device. However, the conventional drive circuit has had a problem of inability to test the semiconductor device unless the heater is formed on it.
This problem is further described below with reference to two examples of the prior art drive circuit.
FIG. 3A
shows in conceptual form a thermal ink-jet head using an exemplary prior art drive circuit in its completed form, and
FIG. 3B
shows the same thermal ink-jet head except that the drive circuit is in an incompleted form. In a recording head
38
shown in
FIGS. 3A and 3B
a drive circuit
40
comprises driver transistors T
11
-T
15
and a control circuit
36
for performing on-off control on these driver transistors T
11
-T
15
. Driver transistors T
11
-T
15
correspond to heat-generating resistors R
11
-R
15
, respectively, which in turn correspond to a plurality of recording elements that perform printing.
The heat-generating resistors R
11
-R
15
are connected at one end to a common ground GND and connected at the other end to sources of the driver transistors T
11
-T
15
. Drains of the driver transistors T
11
-T
15
are connected to a common power supply VD
1
and their gates are supplied with control signals from the control circuit
36
respectively. In the illustrated case, only five recording elements are shown to simplify the explanation.
The control circuit
36
in the illustrated case is a decoder which comprises decoder circuits D
1
-D
5
for decoding signals C
1
-C
4
. The control circuit
36
may be composed of a shift register and other circuits, for instance, as shown in
FIGS. 4A and 4B
. The control circuit
36
in
FIGS. 3A and 3n
is replaced by the shift register
42
in
FIG. 4A
which shows the drive circuit of a thermal ink-jet head in its completed form and in
FIG. 4B
showing the same drive circuit in an incompleted form.
In addition to the shift register
42
for accessing heat-generating resistors R
11
-R
15
, the drive circuit shown in
FIGS. 4A and 43
also has a control signal line CTRL
2
for performing on-off control of the heat-generating resistors R
11
-R
15
, as well as transistors T
31
-T
35
which are switching elements connected to the control signal line CTRL
2
to control connection and non-connection between outputs of the shift register
42
and driver transistors T
11
-T
15
.
In the recording head
38
in completed form which is shown in
FIG. 3A
, for instance, when driver transistors T
11
-T
15
are turned on in response to control signals from the control circuit
36
, current flows through the respectively corresponding heat-generating resistors R
11
-R
15
and a specified amount of ink is projected from nozzles which are the corresponding recording elements. Conversely, if the driver transistors T
11
-T
15
are turned off, no current flows to the heat-generating resistors R
11
-R
15
and no ink is projected from the nozzles.
In the recording head
38
in an incompleted form which is shown in
FIG. 3B
, the heat-generating resistors R
11
-R
15
to be driven are not connected to the drive circuit
40
and the sources of the driver transistors T
11
-T
15
are opened, so it is impossible to check if the drive circuit
40
is operative or not. While the problem with the prior art has been described above with particular reference to the recording head of an ink-jet printer, it should be noted that the same problem exists in all other devices that are furnished with the drive circuit, as exemplified by an LED (light-emitting diode) array, an EL (electroluminescent) panel, a magnetostrictor and other devices.
SUMMARY OF THE INVENTION
An object of the present invention is to solve above described problem based on the prior art to provide a drive circuit that can be tested for reliability after it has been formed on a substrate by the first fabrication process but before a plurality of elements to be driven are formed on the same substrate by the second fabrication process.
Another object of the present invention is to provide a method of testing the drive circuit.
The object of the invention can be attained by a drive circuit that is formed on a substrate by a first fabrication process and that drives a plurality of elements to be driven being formed on the substrate by a second fabrication process which is different from the first fabrication process, comprising driver transistors provided between a first signal line and the plurality of elements to be driven; a control circuit for performing on-off control on the driver transistors; and a test circuit for testing the drive circuit, the test circuit comprising switching elements and resistor elements that are series connected between a second signal line and junctions of the driver transistors and the elements to be driven respectively, wherein the test circuit performs on-off control on the switching elements in response to a control signal.
Preferably, the plurality of elements to be driven are heat-generating resistors, magnetostrictors or light emitters and are connected between each of the driver transistors corresponding to each of the plurality of elements to be driven and the second signal line.
Another object of the invention can be attained by a method of testing a drive circuit that drives a plurality of elements to be driven, the drive circuit comprising a driver transistors provided between a first signal line and the plurality of elements to be driven, a control circuit for performing on-off control on the driver transistors, and a test circuit for testing the drive circuit, the test circuit comprising switching elements and resistor elements that are series connected between a second signal line and junctions of the driver transistors and the elements to be driven respectively, the test circuit performing on-off control on the switching elements in response to a control signal, comprising steps of: forming the drive circuit on a substrate by a first fabrication process; before the plurality of elements to be driven are formed by a second fabrication process which is different from the first fabrication process, on the substrate on which the drive circuit has been formed, turning on the switching elements of the test circuit in response to the control signal; and performing on-off control on the driver transistors by the control circuit.
Preferably, the drive circuit is tested by changing electric potential of the first signal line to either power supply potential or ground potential.
Preferably, the drive circuit is tested by adjusting electric p
Niebling John F.
Stevenson André C
Whitham Curtis & Christofferson, P.C.
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