JPS61279175A - Driving method for charge transfer device - Google Patents

Abstract

PURPOSE:To make it possible to transfer electric charge perfectly at an input part and to improve distortion characteristics, by differentiating the times when the instantaneous levels of two pulses, whose phases are different by about 180 degrees to each other and which are applied to the first and second transfer electrodes, start changing. CONSTITUTION:A pulse phis is applied to a sampling electrode 5. A pulse phi1 is applied to a first transfer electrode 7 and third transfer electrodes 10 and 11. A pulse phi2 is applied to second transfer electrodes 8 and 9. The pulses phi1 and phi2 have the phase difference by about 180 degrees. The relation of potentials at intersections is expressed by V1<V2. When the charge is moved from the part beneath a constant voltage electrode 6 to the part 1 beneath the potential, phi2 is applied to the electrode 8. Therefore, the potential beneath the electrode 8 becomes high so that the charge, which is transferred to the part beneath the electrode 7, is not exceeded. When the charge is transferred to the part beneath the electrode 9 from the part beneath the electrode 7, the potentials beneath the electrodes 7 and 8 become low so that the charge does not flow back to the part beneath the electrode 6. Therefore, the perfect charge transfer can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for driving a charge transfer device, and in particular to a method for driving a charge transfer device.
The present invention relates to a method of driving a charge transfer device called a so-called CCU (charge coupled device) having a type structure.

BACKGROUND TECHNOLOGY CCD uses information on the presence or absence of charges that exist in an unstable state on the silicon surface under the oxide film in the MO8 structure, and applies an appropriate control voltage to the gate electrodes arranged in an array to transfer the charges to the bottom of the gate electrodes. Transfer is performed along the silicon surface, and it is used in shift registers, delay circuits, arithmetic circuits, and even imaging devices.

As an example of such a COD, a two-phase drive CCU using an N-type buried channel is shown in FIG. In Figure 1,
An n,-buried layer 2 is formed on a P-type semiconductor substrate 1 . A charge injection part 3 by Lu+ diffusion is provided adjacent to this n- buried layer 2. An oxide film 4 is formed on the main surface of the semiconductor substrate 1 on which the n-buried layer 2 and the like are provided.

The oxide film 4 has doglegs in thickness at predetermined intervals, and first layer electrodes 5, 7, 9, and 11 made of polysilicon or metal are buried inside the dogged areas. has been done. Still on the surface of the part where the thickness of the oxide film 4 has become small, there is a second layer made of polysilicon or metal similar to the first layer electrode.
Layered electrodes 6, 8, and 30° 12 are formed. The electrode 5 serves as a sampling electrode for determining the timing of charge injection. The electrode 6 is a constant voltage electrode that stores the injected charges. Electrode 7 serves as a first transfer electrode. Further, electrodes 8 and 9 form a second transfer electrode, and electrodes 0 and 11 form a third transfer electrode.

Below the second layer electrodes 6 , 8 , ], 0 , 12 is a barrier section 13 formed by introducing P-type impurities using a self-alignment line using the first layer electrodes 5 , 7 , 9 , 11 as a mask. , 14, 15, and 16 are provided. and,
Electric charges are accumulated under the first layer electrodes 5, 7, 9.11, and under the second layer electrodes 6, 8, 10.12, the barrier portions 13, 14, 15, 16 By raising the potential for electrons below the electrode, backflow of charges is prevented.

According to the conventional driving method of CCD as described above, as shown in FIG.
A pulse φ8 as shown in A) is applied to the first layer electrode 5 as a sampling electrode, and pulses φ1 and φ2 of mutually opposite phases are applied to the electrode 7°10.11 as shown in FIG.
and electrodes 8.9.12, respectively. Pulse φ
1. The waveforms of φ2 are equal and the phases are different from each other by 172 cycles. Then, the potential at the intersection of the rising edge of pulse φ1 and the falling edge of pulse φ1 is equal to the instantaneous level at the rising edge of pulse φ1 and the falling edge of pulse φ. The potential at the intersection of the potential at the falling edge of the pulse φ and the rising edge of the pulse φ2, that is, the potential when the instantaneous levels are equal at the falling edge of the pulse φ1 and the rising edge of the pulse φ2. are equal.

At this time, time 1. -16 CCT) The potential for electrons and the movement of charges (electrons) are shown in Figure 6 (
A) to the same figure (as shown in Pi. That is, time t
At 0, the pulse φ8 becomes high level, and as shown in FIG.
The potential of Flows downward.

Next, when the pulse φ8 becomes low level at time t, the potential under the electrode 5 (between 81 in the same figure) increases as shown in FIG. Then, when the instantaneous level of pulse φ begins to rise by 2 and the instantaneous level of pulse φ2 begins to decrease (time t8),
) as shown below the electrode 7 as the first transfer electrode (UV
The potential below the electrodes 8 and 9 at the end of the second transfer electrode (between vX in the figure) begins to rise.

Then, when the potential under the electrode 7 approaches Vro, the charge under the electrode 6 begins to move under the electrode 7. At this time, the charge exceeds the area below electrode 8 (between VW in the same figure) and the area below electrode 9 (between WX in the same figure).
In order to prevent the potential under the electrode 8 from reaching the voltage (between UV and UV) at time t8, the potential under the electrode 7 is at least lower than the potential under the electrode 7 (between UV in the figure) due to the inflow of charge under the electrode 7. need to be higher than the increase in

At time t, the transfer is completed, and the charge is accumulated under the electrode 7 (between UV and UV in the figure) as shown in Figure 6). Then, as the instantaneous level of pulse φ begins to fall and the instantaneous level of pulse φ begins to rise, the potential under electrode 7 begins to rise and the potential under electrodes 8 and 9 begins to fall. At time t5, the charge under electrode 7 begins to move under electrodes 8 and 9, as shown in ) in FIG. 6, but at this time, the potential relationship is equal to that at time t8.
Since the potential under the electrode 7 becomes higher than To at time t6, the electric charge under the electrode 7 is divided into the lower part of the electrode 6 and the lower part of the electrode 9 as shown in FIG. 6 [F] at time t6. As a result, part of the charge flows backward and is lost, causing distortion in the CCD output.

If all the charges under the electrode 7 are transferred to the electrode 9 at time t5,
In order to transfer downward, it is necessary to complete the transfer while the potential under the electrode 7 is at least two steps lower than Fo, as shown in FIG. 7 (C1). However, under such conditions Then time t8
In this case, as shown in FIG. 7(A), the charge under the electrode 6 reaches not only under the electrode 7 but also under the electrode 9. Further, at time t, as shown in FIG. 7(B), the charge under the electrode 6 reaches 1 or more due to a break under the electrode 11 (between Y and Z in the figure). Therefore, part of the charge to be accumulated under the electrode 6 is added to the charge sampled one cycle before. In such a case, distortion will occur in the CCD output and the characteristics will deteriorate.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for driving a charge transfer device that allows complete charge transfer.

The four driving methods of the charge transfer device according to the present invention include applying voltage to first and second transfer electrodes formed on a semiconductor layer of a predetermined conductivity type via an insulating film and arranged sequentially in a predetermined direction following a constant voltage electrode. The present invention is characterized in that the instantaneous levels of the two drive pulses having substantially opposite phases to each other start changing at different times.

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 2 to 4.

By the driving method of the present invention, a pulse φ8 as shown in FIG. 2(3) is applied to the electrode 5 as a sampling electrode, and pulses φ1 and φ2 as shown in FIG.
0.11 and applied to electrodes 8 and 9.12, respectively.

These pulses φ0. φ is obtained, for example, by delaying one of two pulses with opposite phases to each other, and the potential ■ at the intersection of the rising edge of pulse φ and the falling edge of pulse φ is determined by the falling edge of pulse φ1. The potential ■ at the intersection of the edge and the rising edge of the pulse φ2 is higher.

At this time, the pulse φ0. shown in FIG. φ1. At the time corresponding to time t8 when driven by φ2, that is, when the charge is transferred from below the electrode 6 to below the electrode 7, the potential below the electrode 7 approaches the hole, and the charge moves from below the electrode 6 to below the electrode 7. At this time, since φ, whose falling start time is earlier than the rising start time of φ1, is applied to the electrode 8, the potential under the electrode 8 becomes high enough not to be exceeded by the charge transferred to the bottom of the electric box 7. The pulse φ shown in FIG.

, φ0. When driven by φ, the time corresponding to time t, that is, when the charge is transferred from below the electrode 7 to below the electrode 9, the rising start time is earlier than the falling start time of φ1.
.

is applied to the electrode 8, the potential below the electrode 7 and the potential below the electrode 8 is vf to the extent that the charge does not flow back to the bottom of the electrode 6.
It will be lower than o.

Therefore, loss of charge due to backflow and erroneous increase of charge sampled -period ago are prevented, and complete charge transfer is possible.

FIG. 3 shows another embodiment of the invention, in which the potential V1
．． V is equal to the lowest potential and the highest potential of pulses φ□ and φ2. In this case as well, the same operation as in the case of FIG. 2 can be obtained.

FIG. 4 shows yet another embodiment, in which only the pulse φ8 and the pulse φ1 applied to the first transfer electrode are delayed from the case in FIG. Even in such a case, the pulse φ shown in FIG. , φ1. φ.

When the charge moves from below the electrode 6 to below the electrode 8-7, the potential below the electrode 8 becomes high enough not to be exceeded by the charge transferred below the electrode 7. Also, when the charge is transferred from below the electrode 7 to below the electrode 9, the potential below the electrode 7 and the potential below the electrode 8 is
It becomes lower than Fo to such an extent that reverse flow does not occur, allowing complete charge transfer.

Effects of the Invention As detailed above, the method for driving a charge transfer device according to the present invention includes first and second transfer electrodes formed on a semiconductor layer -F of a predetermined conductivity type with an insulating film interposed therebetween and arranged sequentially in a predetermined direction. Since the times at which the instantaneous levels of the two applied pulses, which are approximately opposite in phase to each other, begin to change are different, this enables perfect charge transfer at the input section and greatly improves the distortion characteristics of the CCD. . Still, the optimum value of the voltage applied to the constant voltage electrode is the pulse φ1. The voltage V0 at the intersection of φ2. V
, and as the voltages Vl and V2 fluctuate, the optimal value of the voltage applied to the constant-voltage electrode also changes, but since the voltages Vt and V vary due to variations in wafer process conditions, the constant-voltage electrode If the applied voltage is fixed, the yield will be extremely poor and process control will be difficult. However, if the pulse shown in Fig. 3 is used, V,
, V2 does not change even if process conditions vary, yield is greatly improved, and process conditions can be easily controlled.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing the structure of a CCD, Fig. 2 is a waveform diagram showing one embodiment of the present invention, Fig. 3 is a waveform diagram showing another embodiment of the invention, and Fig. 4 is a waveform diagram showing another embodiment of the invention. , a waveform diagram showing still another embodiment of the present invention, FIG. 5 is a waveform diagram showing a conventional driving method, and FIGS. 6 and 7 show a CCD when driving pulses according to the conventional driving method are used. FIG. 3 is a diagram showing internal potential. Bio for 1 Generation = 1 Co., Ltd. Agent Patent Attorney Motohiko Fujimura Figure 7 #-2 Concave Leaf 1 Oro Illustrated Funeral, Figure 7

Claims (1)

[Claims] A semiconductor layer of a predetermined conductivity type, a means for injecting a charge according to an input into the semiconductor layer, a constant voltage electrode formed on the semiconductor layer with an insulating film interposed therebetween, and a constant voltage electrode formed on the semiconductor layer with an insulating film interposed therebetween. first and second transfer electrodes are formed by applying a predetermined voltage to the constant voltage electrode and are sequentially arranged in a predetermined direction following the constant voltage electrode, and the surface of the semiconductor layer under the constant voltage electrode is The injected charges are temporarily stored in the first and second transfer electrodes, and two driving pulses having substantially opposite phases are applied to the first and second transfer electrodes to cause the injected charges to be transferred along the surface of the semiconductor layer under the first and second transfer electrodes. 1. A method for driving a charge transfer device that performs sequential transfer, characterized in that the instantaneous levels of the two drive pulses start changing at different times.