JPH0519828B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to semiconductor devices, and particularly to a signal readout device for a two-dimensional infrared sensor that can suppress unnecessary components caused by background light and the like.

(b) Conventional technology and problems A typical hybrid two-dimensional sensor (IRCCD), which is constructed by combining an infrared photodiode and a two-dimensional (interlaced) CCD, detects background light and other signals for the signal components to be detected. Since the direct current component is large, it is difficult to increase the detection sensitivity and it is difficult to increase the dynamic range. That is, in the infrared sensor, in many cases, the DC component corresponding to the temperature level of the target sample or the ambient temperature, which is background light, is overwhelmingly larger than the signal corresponding to the variation in the temperature of the target sample to be detected. For example, if the temperature of the target sample to be detected varies by a few degrees from room temperature, the detected infrared intensity will be the background light corresponding to approximately 300 [〓], and the weak infrared intensity corresponding to a change of only a few degrees. Correspondingly, the detection output is a DC component corresponding to the background light and a weak signal component superimposed thereon. Therefore, in order to improve the detection sensitivity, it is necessary to remove the above-mentioned DC component and extract only the desired signal component.

However, if an attempt is made to add a function to suppress the direct current component due to such background light to the readout circuit of a conventional two-dimensional infrared sensor, the configuration of the readout circuit becomes complicated and the area of the CCD region decreases.
Therefore, the emergence of a truly practical infrared sensor readout circuit has been strongly desired.

(c) Purpose of the Invention The present invention has been made in view of the above circumstances, and its purpose is to suppress DC components caused by background light, etc. and extract only desired signal components, and to have a simple configuration. An object of the present invention is to provide a readout circuit for a two-dimensional infrared sensor.

(d) Structure of the invention The present invention inputs the detection output of a photoelectric conversion element,
In a semiconductor device having a configuration including a readout charge amount control element that selects a required signal portion from the input and outputs it to a CCD and discharges an unnecessary charge portion to a reset transistor, the readout charge amount control element is a one-conductivity type semiconductor substrate. It has input side and output side opposite conductivity type regions formed on the surface to be spaced apart from each other, and an input gate, an accumulation gate, and a transfer gate on a region sandwiched between the input side and output side opposite conductivity type regions. ,
The input side reverse conductivity type region is connected to the output terminal of the photoelectric conversion element, and the output side reverse conductivity type region is connected to the source terminal of the reset transistor and the input terminal of the CCD, and the input gate , selectively controlling the potentials of the storage gate and the transfer gate to output a required signal portion of the detection output of the photoelectric conversion element from the output side reverse conductivity type region to a CCD in time series, or This semiconductor device is capable of discharging an unnecessary charge portion to a reset transistor.

(e) Embodiment of the Invention An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view schematically showing the main parts of an embodiment of the present invention, in which 1 is a readout charge amount control element, 2 is a CCD, 3 is a reset transistor,
Reference numeral 4 denotes a photoelectric conversion element, which in this embodiment is an infrared photodiode. Furthermore, 5 is a semiconductor substrate of one conductivity type, in this example, a p-type silicon (Si) substrate, 6, 7,
8, 9, and 9' are regions of opposite conductivity type, and in this embodiment are n-type regions; 10 is an insulating film, such as a silicon dioxide (SiO ₂ ) film; and 11, 12, and 13 are readout charge amount control layers made of polycrystalline silicon, etc. The input gate, storage gate, and transfer gate of element 1, 14 and 15 are
Transfer gate and transfer electrode of CCD 2, 16 is the gate electrode of reset transistor 3, 14-16
Both are made of polycrystalline silicon. Furthermore, CCD
2. The reset transistor 3 and infrared photodiode 4 are no different from ordinary ones.

The operation of this embodiment is comprised of three stages: charge accumulation, signal readout, and unnecessary charge discharge.
The operation will be explained with reference to the potential diagram in FIG.

First, input gate 1 of readout charge amount control element 1
1, a DC voltage of approximately 0.1 [V] is applied throughout the entire period. As a result, as seen in FIG. 2, the potential directly below the input gate 11 is pushed down slightly.

[Charge Accumulation] (See Figure 2a) In the above state, a pulse voltage of about 10 [V] is applied to the accumulation gate 12. At this time, transfer gate 1
The potential of point 3 is set to 0 [V]. As a result, the potential directly below the storage gate 12 is pushed down much deeper than the potential 22 directly below the input gate 11, and the potential well 20
is formed, an amount of charge corresponding to the detected infrared light intensity flows from the infrared photodiode 4 into the potential well 20 via the n-type region 6 (arrow A), and continues for a predetermined time. After the elapse of time, an amount of charge 21 corresponding to the intensity of the infrared light is accumulated in the potential well 20. Since no voltage is applied to the transfer gate 13 at this stage, the potential directly below it remains high and acts as a barrier 23 between the potential well 20 and the n-type region 7. Therefore, the charge within the potential well 20 does not flow out.

[Signal readout] (see figure b) Next, a pulse voltage of approximately 2 [V], for example, is applied to the transfer gate 13 of the readout charge amount control element 1, and a voltage of approximately 3 [V] is applied to the transfer gate 14 of the CCD 3. Apply. As a result, the potential directly below the transfer gates 13 and 14 is lowered, and the barriers 23 and 24 are lowered. Therefore, of the charge 21 accumulated in the potential well 20, the portion higher than the potential of the barrier 23 crosses the barriers 23 and 24 and becomes the CCD 2.
into the potential well 25 (arrow B,
C) Do.

[Unnecessary Charge Discharge] (See c in the same figure) Next, the voltage applied to the transfer gate 14 of the CCD 2 is set to 0 [V], the barrier 24 is raised, and the transfer of charges to the CCD 2 is stopped. And CCD2
By applying a predetermined voltage to the transfer electrode 15 according to the normal readout method,
The charges accumulated in the potential well 25 are transferred and read out as time series data.

On the other hand, in the readout charge amount control element 1, the voltage applied to the storage gate 12 is set to about 1 [V] to increase the potential directly below the storage gate 12, and the voltage applied to the gate 16 of the reset transistor 3 is set to about 3 [V]. By lowering the potential 26 directly below the gate 16 by applying a voltage, the charge remaining inside the potential well 20 is removed via the n-type region 7 and the n-type regions 9, 9' of the reset transistor 3. and flows out to an external power source (arrows D and E). As a result, unnecessary charges within the potential well 20 are discharged.
After emptying the potential well 20 in this manner, the above-described operations are repeated in sequence.

In the above description, the amount of charge accumulated in the potential well 20 during the charge accumulation stage corresponds to the temperature of the target sample to be detected. That is, in the example given in the description of the conventional example, an amount of charge corresponding to approximately 300 [〓] is accumulated. The amount of charge in the potential well 20 is represented by the height of the hatch 21 in the figure.

In this embodiment, in the next signal readout step, by selecting the voltage applied to the transfer gate 13 and controlling the height of the barrier 23, the CCD 2 is selected from the amount of charge accumulated in the potential well 20. The amount of charge transferred to can be controlled. For example, if the height of the barrier 23 is 280 [〓], the amount of charge transferred to the CCD 2 is:
The amount is only equivalent to approximately 20 [〓] signals, and the above
Unnecessary charges corresponding to the 280 [〓] signal will be discharged to the outside.

As described above, by using this embodiment, it is possible to remove undesirable DC components from the detection output of the infrared sensor and read out only the desired signal portion.

FIG. 3 is a plan view of essential parts showing an example of the configuration of the signal readout section of the above embodiment, and the same parts as in FIG. 1 are designated by the same reference numerals.

As described above, the signal readout section of this embodiment includes the readout charge amount control element 1, the CCD 2, and the reset transistor 3. Although only one readout charge amount control element 1 is shown in the figure, it is actually arranged in a matrix of n rows and m columns, and the CCD 2
One reset transistor 3 is provided for each row of the matrix.

Input gate 1 of the readout charge amount control element 1
1. One storage gate 12 and one transfer gate 13 are provided for each column of the matrix.

31 and 32 are electrode windows opened in the insulating film covering the opposite conductivity type regions 6 and 7, and 33 and 34 are electrodes on the opposite conductivity type region 8 of the CCD 2 and the opposite conductivity type region 9 of the reset transistor 3, respectively. It's a window. Reference numeral 35 denotes a wiring that is led out from the electrode window 35 of the reset transistor 3 and connects the electrode window 32 of all the readout charge amount control elements 1 and the electrode window 33 of the CCD 2 in the corresponding row, and is made of a material such as aluminum (Al). It is formed using a thin metal layer.

Although the above embodiment shows an example in which the Si substrate 5 is of p-type and the region of the opposite conductivity type is of n-type, these may all be reversed.

(f) Effects of the Invention As described above, according to the present invention, when reading out a two-dimensional infrared sensor, it is possible to suppress DC components caused by background light and the like and extract only desired signal components.

[Brief explanation of the drawing]

1 to 3 are diagrams showing one embodiment of the present invention. FIG. 1 is a cross-sectional view of a main part schematically showing the structure of the above-mentioned embodiment, and FIG. 2 is a cross-sectional view for explaining its operation. The potential diagram, FIG. 3, is a plan view of the main parts showing the planar arrangement thereof. In the figure, 1 is a readout charge amount control element, 2
is a CCD, 3 is a reset transistor, 4 is a photoelectric conversion element, 5 is a semiconductor substrate of one conductivity type, 6, 7,
8, 9, 9' are opposite conductivity type regions, 10 is an insulating film, 1
1, 12, and 13 are input gates, storage gates, and transfer gates made of polycrystalline silicon or the like of the readout charge amount control element 1, respectively; 14 and 15 are transfer gates and transfer electrodes made of polycrystalline silicon or the like of the CCD 2; 16 is the gate electrode of the reset transistor 3, 20 and 25 are potential wells, 21 is the accumulated charge, 22, 23,
24 and 26 are potential barriers, and A to E are arrows indicating the direction of charge flow.

Claims (1)

[Claims] 1. In a semiconductor device having a configuration including a readout charge amount control element that inputs the detection output of a photoelectric conversion element, selects a required signal portion of the input, outputs it to a CCD, and discharges an unnecessary charge portion to a reset transistor. The readout charge amount control element has an input side and an output side opposite conductivity type regions formed on the surface of a semiconductor substrate of one conductivity type, and an input gate on a region sandwiched between the input side and output side opposite conductivity type regions. ,
It has an accumulation gate and a transfer gate, and the input side opposite conductivity type region is connected to the output terminal of the photoelectric conversion element, and the output side opposite conductivity type region is connected to the source terminal of the reset transistor and the
By selectively controlling the potentials of the input gate, storage gate, and transfer gate, the detection output of the photoelectric conversion element is changed over time from the output-side opposite conductivity type region to the input terminal of the CCD. A semiconductor device characterized in that it is capable of outputting a required signal portion to a CCD or discharging an unnecessary charge portion to a reset transistor.