JP2965568B2 - Charge detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a method of transferring electric charges transferred by a charge transfer unit including a plurality of electrodes integrated on a semiconductor substrate through floating electrodes. The present invention relates to a charge detection device that converts a voltage into a voltage and detects the voltage.

(Prior Art) FIG. 2 shows a conventional charge detection device. In FIG. 2, an n-type diffusion layer 18 is formed on a p-type substrate 19, and a polysilicon layer 2 is formed on the n-type diffusion layer 18 via an insulating film 20.
Electrodes 12 to 16 having a layer structure are formed. Then, in order to form a potential barrier (about −2 V) between the second layer polysilicon electrode and the first layer polysilicon electrode, an n-type diffusion layer 18 below the second layer polysilicon electrode is formed. Boron ions are implanted to form the n ⁻ layer 21. Also, the first layer polysilicon electrode and the second layer polysilicon electrode are overlapped in order to guarantee charge transfer with respect to a pattern shift when the electrodes are formed.

The output gate electrode 14 is connected to a +4 V DC power supply. The floating electrode 13 is connected to a +5 V DC power supply 24 via a switch 22. When the switch 22 is ON, the floating electrode 13 is fixed at +5 V, and when the switch 22 is turned OFF, the floating electrode 13 is in a non-connected (floating) state. An n ⁺ diffusion layer 17 is connected to the left end of the n-type diffusion layer 18, and the diffusion layer 17 is connected to the +11 V D
Fixed to + 15V by C power supply. The right side of FIG. 2 is connected to a charge transfer unit, and electrodes 15 and 16 represent two electrodes at the ends of the charge transfer unit. The charges transferred by the charge transfer section are transferred in the direction of the arrow (right to left) shown in FIG.

FIG. 3 shows a potential diagram. The vertical axis indicates the potential, and the horizontal axis indicates the position. The positions (signs) shown on the horizontal axis correspond to the signs of the electrodes shown in FIG. FIG. 4 shows pulses applied to the electrodes 16, 15, 12 and the switch 22, and the potential of the electrode 13.
Charges transferred through the charge transfer section from Figure 2 the right are accumulated under the electrode 15a, the time t ₁ as shown in FIG. 4
When the electrode 15 changes from H to L, the data is transferred as indicated by arrows A, B, and C shown in FIG. When electrode 12 is L → H at time t ₂ shown in FIG. 4, the floating electrode
The charges under 13 are discharged to the n ⁺ diffusion layer 17. Floating electrode
When electric charge flows below 13, the potential of the electrode 13 decreases. Since the floating electrode 13, the electrode 12, and the electrode of the switch 22 are capacitively coupled, the potential of the floating electrode 13 changes as shown in FIG. And in between times t ₁ and t _2, by sampling the potential can be detected charge amount as a voltage variation. Note that no electric charge is accumulated under the electrode 14, and serves to localize the electric charge under the floating electrode 13.

FIG. 5 shows a circuit connection diagram around the floating electrode 13. As described above, when charge flows into the n-type diffusion layer 18 with the switch 22 turned off, the potential of the floating electrode 13 drops. This voltage drop is amplified and output by the amplifier 41 having a high input impedance. At this time, the change in the voltage corresponding to the amount of charge input to the amplifier 41 is determined by the capacitance value connected to the floating electrode 13. FIG. 6 shows these capacitance values.

C ₁ represents the capacitance between the channel -p-type substrate 19 in FIG. 6. C ₂ indicates a capacitance between the channel and the floating electrode 13, and the capacitance C ₂ mainly includes a component expressed as a series coupling of the capacitance between the channel and the interface and the capacitance of the oxide film under the electrode. C ₄
Is the capacitance between the floating electrode 13 and the p-type substrate 19, which is mainly based on the wiring capacitance of the floating electrode 13, the input capacitance of the switch 22, the input capacitance of the amplifier 41, and the capacitance due to the overlap between the floating electrode 13 and other electrodes. Become. In particular, the capacitance C ₄ due to the overlap between the floating electrode 13 and the output gate electrode 14 shown in FIG.
It is one of the main components of C _3.

(Problems to be Solved by the Invention) During the capacitance C ₁ and C ₂ shown in FIG. 6 is a channel. Here, assuming that a potential change when the charge Q flows in is ΔV ₁ and a change in the input voltage of the amplifier 41 is ΔV ₂ , Becomes Here, when C ₁ << C ₃ and C ₁ << C ₂ , Next, the capacitance C ₃ to determine the charge-to-voltage conversion ratio. In the conventional charge detecting device as shown in Figure 2, a major component of the capacitance capacitor C ₃ by overlap of the electrodes 13 and other electrodes as described above, because they become large, the charge voltage The conversion ratio is reduced and the amplifier shown in FIG.
Due to the noise in 41, there was a problem that the S / N ratio of the output signal was reduced.

The present invention has been made in consideration of the above problems, and has as its object to provide a charge detection device capable of increasing the charge-to-voltage conversion ratio as much as possible.

[Configuration of the invention]

(Means for Solving the Problems) The present invention converts a charge transferred by a charge transfer section composed of a plurality of electrodes of an overlapping gate structure integrated on a semiconductor substrate into a voltage via a floating electrode and detects the voltage. In the charge detection device, a gap is provided between the last-stage electrode of the charge sending unit and the floating electrode, and a depletion potential under this gap is set when a pulse applied to the last-stage electrode is at a high level. Adjusting the impurity concentration under the gap so as to be a value between a potential generated under the electrode at the last stage and a potential generated under the electrode at the last stage when the pulse is at a low level; Has no control electrode.

Further, according to the present invention, there is provided a charge detecting device for converting a charge transferred by a charge transfer unit including a plurality of electrodes having an overlapping gate structure integrated on a semiconductor substrate into a voltage via a floating electrode and detecting the charge, A gap without a control electrode is provided immediately above the last-stage electrode of the transfer unit and the floating electrode, and the electric charge accumulated under the last-stage electrode passes through a region below the gap at a predetermined timing. And accumulated under the floating electrode.

(Operation) According to the charge detection device of the present invention configured as described above, a gap is provided between the electrode at the last stage of the charge transfer section and the floating electrode, and the depletion potential below the gap becomes a predetermined value. Thus, the impurity concentration below the gap is adjusted. As a result, a predetermined depletion potential is formed below the gap, and the charge transferred from the charge transfer unit is localized under the floating electrode. The capacitance C ₃ between the floating electrode and the semiconductor substrate is reduced by providing the gap between the electrode of the final stage of the charge transfer portion and the floating electrode, so that the charge-voltage conversion ratio is improved.

(Embodiment) FIG. 1 shows an embodiment of a charge detection device according to the present invention.
The charge detection device of this embodiment is different from the conventional charge detection device shown in FIG. 2 in that the output gate electrode 14 is deleted to provide a gap between the electrode 15a at the last stage of the charge transfer section and the floating electrode 13, N ^- diffusion layer 2 formed under electrodes 15b and 16b of the charge transfer section
Boron ions are implanted below the gap to form an n ⁻ layer 61 so as to have a concentration lower than the n-type impurity concentration of 1. Since the n ⁻ layer 61 has a lower impurity concentration than the n ⁻ layer formed under the electrode of the charge transfer section,
The gap has a predetermined depletion potential without electrodes. Now, n ^- if the impurity concentration of the layer 61 is appropriately adjusted so that the depletion potential under the gap becomes 10V, the potential diagram of this embodiment is the electrode 14 in Figure 3 ^- and n layer 61 It will be.

Also, by providing a gap between the last-stage electrode 15a and the floating electrode 13 of the charge transfer section, the overlap between the floating electrode 13 and the last-stage electrode 15a is eliminated, and the floating electrode 13 and the p-type substrate 19 capacitance C ₃ is to be reduced between. As a result, the charge-to-voltage conversion ratio is improved, and for example, a decrease in the S / N ratio due to noise of the amplifier 41 shown in FIG. 5 can be suppressed.

〔The invention's effect〕

According to the present invention, the charge-voltage conversion ratio can be made as high as possible.

[Brief description of the drawings]

1 is a sectional view showing an embodiment of a charge detecting device according to the present invention, FIG. 2 is a sectional view of a conventional charge detecting device, and FIG. 3 is a potential diagram of the charge detecting device of the charge detecting device shown in FIG. , Fourth
FIG. 5 is a timing chart of a pulse applied to each electrode of the charge detection device shown in FIG. 2, FIG. 5 is a connection diagram around the floating electrode, and FIG. 6 shows a capacitance corresponding to the connection diagram shown in FIG. It is a schematic diagram. 11 ... Electric discharge electrode, 12 ... Reset electrode, 13 ...
Floating electrode, 14 ... Output gate electrode, 15,16 ... Charge transfer electrode, 13,15a, 16a ... Charge transfer electrode of first layer polysilicon, 12,15b, 16b ... Second layer polysilicon Charge transfer electrode, 17 ... n ⁺ diffusion layer, 18 ... n-type diffusion layer, 19
... p-type substrate, 20 ... insulating layer, 21 ... n ^- diffusion layer, 22 ...
MOS switch, 24 ...... 5V power supply voltage setting of the floating diffusion electrode, 41 ...... high input impedance of the amplifier, 61 ...... n ^-
Diffusion layer.

Claims (3)

(57) [Claims] 1. A charge detection device for detecting a charge transferred by a charge transfer unit comprising a plurality of electrodes having an overlapping gate structure integrated on a semiconductor substrate by converting the charge into a voltage via a floating electrode. A gap is provided between the last-stage electrode of the transfer unit and the floating electrode, and the depletion potential under this gap is below the last-stage electrode when the pulse applied to the last-stage electrode is at a high level. The impurity concentration under the gap is adjusted so as to be a value between the generated potential and a potential generated under the electrode in the final stage when the pulse is at a low level, and a control electrode is provided on the gap. A charge detection device, characterized in that there is no charge detection device. 2. A charge detecting device for converting charges transferred by a charge transfer portion comprising a plurality of electrodes of an overlapping gate structure integrated on a semiconductor substrate into a voltage via a floating electrode and detecting the voltage, A gap without a control electrode is provided immediately above the last-stage electrode of the transfer unit and the floating electrode, and the electric charge accumulated under the last-stage electrode passes through a region below the gap at a predetermined timing. A charge detection device which is stored under the floating electrode. 3. The semiconductor device according to claim 2, wherein the channel region under the electrode at the last stage of the charge transfer section and the channel region under the floating electrode are of a conductivity type opposite to that of the semiconductor substrate, and the impurity region under the gap is separated from the semiconductor substrate. 3. The semiconductor device according to claim 1, wherein said channel region is of a reverse conductivity type and has a lower impurity concentration than said two channel regions.
The charge detection device according to claim 1.