The present invention relates to a MIS (metal-insulator-semiconductor) device (including MISFET (metal-insulator-semiconductor field-effect-transistor) and CCD (charge-coupled-device) structures), an analogue MISFET using MIS device, a threshold voltage correcting method using MIS device, a potential adjusting method using MIS device, a bias circuit using MIS device, a charge transfer device using MIS device, a solid-state imaging device using MIS device and a charge detecting apparatus using MIS device.
More particularly, this invention relates to a MIS device in which a threshold voltage or channel potential can be controlled in an analogue fashion.
This invention relates to a method of correcting a threshold voltage in which a fluctuation of a threshold voltage between MIS devices of a semiconductor integrated circuit composed of a plurality of MIS devices can be corrected.
This invention relates to a method of adjusting a channel potential in which a channel potential of a MIS device can be adjusted.
This invention relates to a bias circuit in which an output bias can be set in an analogue fashion.
This invention relates to a charge transfer device using a CCD.
This invention relates to a solid-state imaging device, such as a CCD solid-state imaging device and an amplifying-type solid-state imaging device.
This invention relates to a charge detecting device used in a solid-state imaging device.
CCD solid-state imaging devices have an imaging region composed of an n-type semiconductor substrate, a p-type well region formed on the n-type semiconductor substrate and a plurality of n-type photoelectric conversion portions, i.e., light-receiving portions formed on the p-type well region in a matrix fashion.
In the above CCD solid-state imaging device, an allowable amount of signal charges e accumulated in the light-receiving portion when light becomes incident on the light-receiving portion, i.e., an amount of signal charges treated by the light-receiving portion is determined by a height of a potential barrier .phi..sub.a of an overflow barrier OFB composed of the p-type well region as shown in potential distribution diagrams of FIGS. 1A and 1B. Specifically, if the signal charges e accumulated in the light-receiving portion exceeds the amount of signal charges treated by the light-receiving portion, then extra charges are overflowed through the potential barrier .phi..sub.a, of the overflow barrier OFB and discharged to the n-type substrate forming an overflow drain OFD.
The amount of signal charges treated by the light-receiving portion, i.e., the height of the potential barrier .phi..sub.a of the overflow barrier OFB is controlled by a bias voltage applied to the n-type substrate forming the overflow drain OFD, i.e., so-called substrate voltage V.sub.sub. However, according to this device structure, since device structures are frequently fluctuated when they are manufactured, the height of the potential barrier .phi..sub.a. of the overflow barrier OFB is frequently fluctuated as shown by a dotted line height .phi..sub.a in FIG. 1A. Therefore, each time devices are manufactured, different substrate voltages V.sub.sub, V.sub.sub ' have to be set, respectively.
In the CCD solid-state imaging device, as shown in FIG. 2, a floating diffusion region FD for converting electric charges into voltages is formed at the succeeding stage of a horizontal transfer register 1 through a horizontal output gate portion HOG. There are provided a reset gate portion 2 and a reset drain region 3 for resetting signal charges transferred to the floating diffusion region FD at every pixel.
The horizontal transfer register 1 is composed of an n-type transfer channel region 5 formed on the surface of the p-type well region 4, for example, a gate insulating film and a plurality of transfer electrodes 6 [6A, 6B]. The adjacent two transfer electrodes 6A and 6B are paired. Two-phase horizontal drive pulses .phi.H.sub.1 and .phi.H.sub.2 are applied to every pair of transfer electrodes 6 [6A, 6B] and every other pair of transfer electrodes 6 [6A, 6B]. A p-type region 7, for example, is formed on the transfer channel region 5 under each second transfer electrode 6B by implantation of ions thereby to form a transfer portion including a storage electrode formed of the first transfer electrode 6A and a transfer portion formed of the second transfer electrode 6B.
The horizontal output gate portion HOG is composed of the gate insulating film (not shown) and a gate electrode 8 formed thereon through the gate insulating film. A ground potential is applied to the gate electrode 8. The floating diffusion region FD is formed of an n-type semiconductor region, for example, and connected to a charge detector 9 whose detected output signal is obtained at an output terminal t.sub.1. The reset drain region 3 is formed of an n-type semiconductor region, for example, and a reset voltage V.sub.RD, e.g., a power supply voltage V.sub.DD is applied to the reset drain region 3.
The reset gate portion 2 is composed of the gate insulating film (not shown) and a gate electrode 10 formed thereon through the gate insulating film. A reset pulse .phi..sub.RG is applied to the gate electrode 10.
In recent CCD solid-state imaging devices, a driver circuit for applying the drive pulses .phi.H.sub.1, .phi.H.sub.2 is incorporated in the horizontal transfer register 1 and a driver circuit for applying the reset pulse .phi..sub.RG is incorporated in a timing generator. Moreover, in order to reduce a power consumption, an amplitude of a pulse is lowered.
Since an operation point of the reset pulse .sub.100 RG is determined depending on the power supply voltage V.sub.DD which is the reset voltage V.sub.RD, there is then the problem that a potential under the reset gate portion 2 is fluctuated (shown by a dotted line in FIG. 2). To solve this problem, a DC bias value of the reset pulse .phi..sub.RG has to be set to a desired value for every device. The DC bias value of the reset pulse .phi..sub.RG is set by an external circuit (i.e., so-called bias circuit). When the driver circuit for applying the reset pulse .phi..sub.RG is incorporated within the timing generator, the DC bias value of the reset pulse .phi..sub.RG is digitally set in a so-called phase-cut fashion.
Further, an amplifying type solid-state imaging device is known as a solid-state imaging device. The amplifying type solid-state imaging device accumulates photoelectrically-converted holes (signal charges) in a p-type well region of an n-channel MOS (metal-oxide-semiconductor) transistor and outputs a change of channel current based on a potential fluctuation (i.e., potential change in the back-gate) in the p-type well region as a pixel signal. An n-type well region is formed on a p-type substrate and the p-type well region in which signal charges are accumulated. This amplifying type solid-state imaging device also has to set a substrate voltage.
On the other hand, there is known an ultraviolet-light-erasure ROM (read-only memory) having a gate insulating film formed of an SiN film to memorize data by controlling a potential. FIG. 3 shows an example of such ultraviolet-light-erasure ROM. As shown in FIG. 3, a p-type region 11 has an n-type source region 12 and an n-type drain region 13 formed on its surface. A gate electrode 17 made of polycrystalline silicon, for example, is formed between the n-type source region 12 and the n-type drain region 13 through a gate insulating film 16 composed of a silicon oxide film 14 and a silicon nitride film 15. Electrons or holes are accumulated in the silicon nitride film 15 to achieve a memory effect. However, this ROM can be turned on and off in a digital fashion. Therefore, when the SiN layer and the gate electrode contact with each other, injected electric charges e' tend to be leaked to the gate portion and a DC bias of this ROM cannot be controlled in an analogue fashion.
Although CCD solid-state imaging devices are products using a potential of a so-called MIS device, the potential of the MIS device is difficult to be controlled and hence manufactured products of the CCD solid-state imaging devices are not uniform in potential. The potential shift has heretofore been avoided by controlling a bias applied from the outside. The same assignee of this application has previously proposed a method in which a fluctuation of potential is measured and adjusted selectively forcibly. The aforesaid ROM is known as the MIS device whose operation point can be changed later. This ROM can be operated in a digital fashion and therefore a potential cannot be adjusted in an analogue fashion.
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