JPH079387Y2 - Charge coupled device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a charge coupled device, and more particularly to a charge coupled device capable of reducing wiring resistance of a transfer electrode of a frame transfer type charge coupled device.

[Conventional technology]

In recent years, in a two-dimensional solid-state imaging device using a charge coupled device,
There is active movement toward higher density and higher resolution. In particular,
A frame transfer type solid-state imaging device using a charge-coupled device is
It is possible to increase the number of pixels in the horizontal direction relatively easily, and it is promising as a high-resolution element in the future.

FIG. 2 is a plan view of a main part of a conventional typical frame transfer type charge coupled device. In the figure, 1 to 3 are vertical register transfer channels, 4 to 7 are channel stoppers, and 8
Reference numerals 12 to 12 are transfer electrodes made of polycrystalline silicon. In this embodiment, the two-layer superposed electrode is used as the transfer electrode, but the superposed electrode is not necessarily required. In such a conventional element, the transfer electrode is formed of polycrystalline silicon that is very elongated in the horizontal direction, and when the element has a large number of pixels, an increase in the resistance and capacitive load of the transfer electrode cannot be avoided.

In the current semiconductor / integrated circuit technology, the minimum size is 1
Since the limit is about μm and the minimum cell size naturally has a lower limit, it is inevitable to increase the chip size in order to increase the number of pixels. In the case of a frame transfer type solid-state image sensor, the transfer electrodes of the photoelectric conversion area and the memory area are usually formed of polycrystalline silicon as described above,
As the chip size increases, the horizontal length of the transfer electrode increases and the electrode resistance increases. By the way, when the 2/3 "optical system is used, it reaches about 9 mm and the 1" optical system reaches about 13 mm. The vertical length of one transfer electrode is about 10 μm. The layer resistance of polycrystalline silicon is 20 to 40Ω, so that the electrode resistance of one transfer electrode reaches 20 kΩ to 40 kΩ. On the other hand, the load capacitance of one transfer electrode is about several tens of pF.

In the frame transfer type solid-state imaging device, the pulse applied to the transfer electrode is usually applied from both ends of the transfer electrode.
However, as described above, since the transfer electrode has high resistance and large capacity, the applied pulse causes waveform distortion in the central portion of the element. That is, since the transfer electrode can be regarded as a distributed constant circuit of resistance and capacitance, the applied pulse has a rounded waveform as it propagates toward the central portion of the element. Therefore, the pulse voltage applied at the end of the transfer electrode is lowered in the central portion of the element, and the phase is out of phase. In the above example, the time constant determined by the resistance and capacitance is several 100 nsec. Therefore, the applied pulse width is 1 μse.
Normal propagation is impossible with pulses of c or less. Such pulse distortion appears as a phenomenon such as a decrease in transfer efficiency and a decrease in transfer charge amount.

[Problems to be solved by the invention]

As described above, in the prior art, the high resistance polycrystalline silicon electrode is used as the transfer electrode of the vertical register, and when the element has a large number of pixels, the time constant is increased together with the increase of the load capacitance. As a result, a very long distributed constant circuit is formed, which causes the inconvenience that the pulse is not normally applied to the central part of the element, which causes undesirable phenomena such as deterioration of transfer efficiency and reduction of signal amount.

An object of the present invention is to provide a charge-coupled device capable of normally propagating a drive pulse by eliminating such a conventional defect.

[Means for solving problems]

According to the present invention, in a charge-coupled device in which a photoelectric conversion region and a signal charge transfer region are shared, and a transfer electrode of the signal charge transfer region is formed of polycrystalline silicon, a metal electrode is provided along a wiring longitudinal direction of the transfer electrode. The transfer electrode and the metal electrode that are formed are connected to each other through a contact hole for each transfer electrode.

[Action]

In the charge-coupled device of the present invention, a metal electrode is connected to and wired to a high-resistance transfer electrode through a contact hole to apparently reduce the resistance of the transfer electrode and reduce pulse propagation distortion.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a main part of an embodiment according to the present invention, and is a plan view of a main part of a photoelectric conversion area or a memory area of a frame transfer type solid-state image pickup device. In the figure, the same numbers as in FIG. 2 indicate the same components. In the figure, 13 to 27 are contact holes provided on the transfer electrodes, and 28 to 32 are wirings of metal such as aluminum. The metal wirings 28 to 32 are formed along the wiring longitudinal direction of the transfer electrodes 8 to 12 made of polycrystalline silicon, and a contact hole is provided in each column of the vertical transfer channels 1, 2 and 3.

The transfer electrode 8 and the metal wiring 28 have contact holes 13, 14, 15
, The transfer electrode 11 and the metal wiring 29 are connected through the contact holes 16, 17, 18 and the transfer electrode 9 and the metal wiring 30 are connected through the contact holes 19, 20, 21. The transfer electrode 12 and the metal wiring 31 have contact holes 22 and 2
The transfer electrode 10 and the metal wiring 32 are connected via contact holes 25, 26, and 27.

Thus, in this embodiment, the transfer electrodes 8 to 12 and the metal wiring 28 are
Since ~ 32 and 32 are electrically wired in parallel, the electrode resistance in the longitudinal direction, that is, the horizontal direction, of the transfer electrode is substantially determined only by the resistance of the metal wiring, and is greatly reduced compared to the conventional element. . On the other hand, the load capacitance of the transfer electrode can be maintained at the same level as the conventional device. As a result,
Even if a pulse is applied to the transfer electrode, the difference in waveform between the central portion and the end portion of the element disappears, and the distortion in the central portion of the element, which is seen in the conventional element, is removed.

In the above embodiments, the contact holes are provided for each vertical transfer channel row, but they may be provided for each vertical transfer channel row. Further, the material of the metal wiring is not limited to aluminum and may be other materials.

[Effect of device]

As described above, according to the present invention, the wiring resistance of the transfer electrodes can be significantly reduced, and the normal propagation of the drive pulse can be performed even when the element has multiple screen elements. In addition, high-speed driving with a vertical register is also possible, making it possible to realize a high-density, high-resolution solid-state image sensor.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a charge coupled device according to the present invention, and FIG. 2 is a diagram showing a conventional charge coupled device. 1 to 3 ... Vertical transfer channel 4 to 7 ... Channel stopper 8 to 12 ... Transfer electrode made of polycrystalline silicon 13 to 27 ... Contact hole provided on the electrode 28 to 32 ... Metal wiring

Claims (1)

[Scope of utility model registration request] 1. A charge-coupled device in which a photoelectric conversion region and a signal charge transfer region are shared, and a transfer electrode in the signal charge transfer region is formed of polycrystalline silicon. In the charge-coupled device, a metal electrode is provided along a wiring longitudinal direction of the transfer electrode. And the transfer electrode and the metal electrode are connected to each other through a contact hole for each charge transfer region.