Active solid-state devices (e.g. – transistors – solid-state diode – Test or calibration structure
Reexamination Certificate
2001-09-18
2002-04-02
Ngô, Ngân V. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Test or calibration structure
C324S12300R, C324S12300R, C324S124000
Reexamination Certificate
active
06365914
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device provided with a built-in minute charge detecting circuit.
Conventionally, there has been a semiconductor device provided with a built-in minute charge detecting circuit for detecting a minute electric charge. When inspecting this semiconductor device, a minute charge generating circuit that serves as an input signal source is arranged near an input terminal of the semiconductor device so as to make an input signal less susceptible to influence of stray capacitance, external noises and the like. An output signal of the minute charge detecting circuit is measured with a minute electric charge given as a signal directly to the input terminal so as to measure the gain, the signal-to-noise ratio or the like of the minute charge detecting circuit.
FIG. 7
shows a semiconductor device
40
with the built-in minute charge detecting circuit and a minute charge generating circuit
50
for inspecting the semiconductor device. As shown in
FIG. 7
, this semiconductor device has a differential amplifier OP, a charge detecting capacitance C
1
, a charge-discharging witch SW
1
and a processing circuit
44
. An inverted input terminal of the differential amplifier OP is connected to an input terminal
41
and a non-inverted input terminal of the differential amplifier OP is connected to a ground GND. The charge detecting capacitance C
1
is connected across an output terminal of the differential amplifier OP and the inverted input terminal of the differential amplifier OP. The charge-discharging switch SW
1
is connected across the output terminal the differential amplifier OP and the inverted input terminal of the differential amplifier OP. The processing circuit
44
processes an output voltage outputted from the differential amplifier OP. The differential amplifier OP, the charge detecting capacitance C
1
and the charge-discharging switch SW
1
constitute a minute charge detecting circuit
43
.
The semiconductor device
40
shown in
FIG. 7
is inspected by inputting an electric charge generated in the minute charge generating circuit
50
to the input terminal
41
of the semiconductor device
40
. An electric charge Q accumulated when a voltage V is applied to the capacitance C is expressed by:
Q=C×V.
Therefore, assuming that an electric charge accumulated in the charge detecting capacitance C
1
of the minute charge detecting circuit
43
is Q
1
, then an output voltage Vo becomes:
Vo=Q
1
/
C
1
,
and the output voltage Vo of the minute charge detecting circuit
43
is inversely proportional to the charge detecting capacitance C
1
. Therefore, unless the capacitance value of the charge detecting capacitance C
1
is reduced, the output voltage Vo becomes a minute voltage since the electric charge Q
1
is a minute charge. As a result, the measurement error increases. For the above reasons, the charge detecting capacitance C
1
of the minute charge detecting circuit
43
is required to have a minute capacitance value of about several picofarads.
Accordingly, when inspecting the minute charge detecting circuit
43
, a stray capacitance added to the input terminal
41
emerges as a disadvantage. Specifically, if an input stray capacitance Cf is added by connecting an input section of the minute charge generating circuit
43
to the input terminal
41
as shown in
FIG. 7
, then a charge quantity Qf out of the minute charge quantity Q given from the minute charge generating circuit
50
is accumulated in the input stray capacitance Cf. As a consequence, the charge quantity Q
1
accumulated in the minute charge detecting capacitance C
1
becomes a difference between the input charge quantity Q and the electric charge Qf accumulated in the stray capacitance as expressed by:
Q
1
=
Q−Qf.
Since the accumulated electric charge Qf increases when the stray capacitance Cf is increased, the electric charge Q
1
becomes significantly reduced from the input charge quantity Q. Therefore, the stray capacitance Cf becomes a factor of a reduction in measurement accuracy.
When inspecting the semiconductor device shown in
FIG. 7
, it cannot be avoided that the stray capacitance Cf due to wiring is added to the input section of the minute charge detecting circuit
43
even if the minute charge generating circuit
50
is arranged near the minute charge detecting circuit
43
to be measured. Furthermore, in order to connect the minute charge detecting circuit
43
to be measured to the minute charge generating circuit
50
that generates an input signal, it is required to provide a connection by means of a socket or probing. Due to addition of the stray capacitance in the connection, the stray capacitance Cf increases to the extent of several picofarads. For the above reason, the accumulated electric charge Qf increases, which decreases the electric charge Q
1
accumulated in the charge detecting capacitance C
1
of the minute charge detecting circuit
43
. Thereby, there has caused a disadvantage that a measurement error of gain is increased. In order to avoid this disadvantage, it is required to provide a setting of:
Cf<<C
1
.
However, the charge detecting capacitance C
1
cannot be increased in the semiconductor device in which the capacitance value of the charge detecting capacitance C
1
amounts to several picofarads in order to obtain a sufficient output voltage. Therefore, the measurement accuracy cannot be increased.
Moreover, when a minute electric charge is inputted as an input signal directly to the input terminal, an impedance of the input wiring portion is high with a high impedance of the input terminal and a high impedance of the input minute electric charge. The above state is susceptible to the influence of external noises, which leads to a disadvantage that the measurement becomes unstable.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a semiconductor device capable of improving accuracy in measurement of a minute charge detecting circuit by suppressing influence of stray capacitance, external noises and the like during test.
In order to achieve the aforementioned object, the present invention provides a semiconductor device a semiconductor device comprising: a minute charge detecting circuit for detecting a minute electric charge; and a test circuit provided between an input terminal of the semiconductor device and an input section of the minute charge detecting circuit, the test circuit having: a charge transforming capacitance for transforming a voltage signal inputted from the input terminal into an electric charge, and an operation mode switchover means for switching over between a normal operation mode in which an electric charge inputted to the input terminal is detected by the minute charge detecting circuit and a test operation mode in which the voltage signal inputted to the input terminal is transformed into an electric charge by the charge transforming capacitance and the transformed electric charge is detected by the minute charge detecting circuit.
According to the semiconductor device having the above-mentioned construction, the charge transforming capacitance (capacitor) and the operation mode switchover means are provided between the input section of the minute charge detecting circuit and the input terminal of the semiconductor device, and the charge transforming capacitance eliminates the harmful influence of stray capacitance and external noises added to the input terminal.
Specifically, even if stray capacitance attributed to wiring from an input signal source to the input terminal or stray capacitance due to contact of a socket or a probe is added, a high voltage can be applied as a test signal to the input terminal because of the charge transforming capacitance. Consequently, the electric charge accumulated in the charge detecting capacitance in the minute charge detecting circuit is not reduced by the harmful influence of the stray capacitance, and therefore the gain of the minute charge detecting circuit can be accurate
Ngo Ngan V.
Sharp Kabushiki Kaisha
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