Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Charge transfer device
Reexamination Certificate
1996-09-16
2001-07-24
Ngô, Ngân V. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Charge transfer device
C257S233000, C348S303000, C348S304000, C348S319000
Reexamination Certificate
active
06265736
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an image pick-up apparatus, comprising an image sensor with a plurality of gate electrodes which define light-sensitive elements in a semiconductor body which convert incident radiation into collected charge carriers, and also comprising a control circuit for the gate electrodes. The invention also relates to an X-ray examination apparatus comprising such an image pick-up apparatus.
2. Description of the Related Art
An image pick-up apparatus of this kind is known from United States Patent Specification U.S. Pat. No. 4,926,225. The known image pick-up apparatus comprises an image sensor with light-sensitive elements in a semiconductor body which are separated by gate electrodes, thus forming a so-called charge-coupled device (CCD) image sensor. When light radiation is incident on a photosensitive element, electric charges are released at the area of said element by absorption of light quanta and collected as a charge package with an amount of charge which corresponds to the intensity of the incident light radiation. The photosensitive elements together pick up a light image by conversion into a charge carrier image, the brightness value in a pixel of the light image corresponding to the charge in a corresponding light-sensitive element. The prior-art image pick-up apparatus comprises the control circuit in order to adjust the electric voltage applied to the gate electrodes in conformity with a selected mode of operation of the image pick-up apparatus. The region of a light-sensitive element wherefrom charges are collected extends from the charge collection region of the light-sensitive element in the depth direction of the semiconductor body. The depth of the region wherefrom charge is collected can be influenced by adjustment of the gate voltage. In order to reduce crosstalk between neighboring light-sensitive elements, notably for radiation having a comparatively long wavelength such as, for example infrared light, in a prior-art image pick-up apparatus the depth of the regions of the light-sensitive elements wherefrom charge is collected is reduced as the wavelength of the incident radiation is longer, and hence the penetration depth of the incident radiation is greater. The charge released by deeply penetrating radiation which is incident on a light-sensitive element is thus prevented from being collected in a neighboring light-sensitive element where it would cause crosstalk. Consequently, during operation of the known image pick-up apparatus crosstalk is avoided when incident image-carrying radiation of great penetration depth is picked up. The lateral dimensions of the light-sensitive elements of the described image pick-up apparatus, however, cannot be influenced and the spatial resolution of the described image pick-up apparatus cannot be adapted; moreover, it is not possible to increase the spatial resolution, if desired, other than by replacement of the entire image sensor.
SUMMARY OF THE INVENTION
It is inter alia an object of the invention to provide an image pick-up apparatus which comprises an image sensor with a plurality of light-sensitive elements whose spatial resolution can be adjusted.
This object is achieved by means of an image pick-up apparatus according to the invention which is characterized in that the control circuit is arranged to adjust the active surface area of the light collecting surfaces by adjustment of electric voltages to be applied to gate electrodes.
A preferred embodiment of an image pick-up apparatus according to the invention is characterized in that the control circuit is arranged to select a first group of gate electrodes as isolating gate electrodes by adjustment of electric voltages which are to be applied to the gate electrodes of the first group and having a polarity which is the same, relative to electric voltages on gate electrodes which are situated adjacent the gate electrodes of the first group and which do not form part of the first group, as the polarity of the charge carriers collected in the light-sensitive elements.
A further preferred embodiment of an image pick-up apparatus according to the invention is characterized in that the control circuit is arranged to select a second group of gate electrodes as collecting gate electrodes by adjustment of electric voltages to be applied to the gate electrodes of the second group and having a polarity which, relative to electric voltages on gate electrodes which are situated adjacent the gate electrodes of the second group and which do not form part of the second group, opposes the polarity of the charge carriers collected in the light-sensitive elements.
In an image pick-up apparatus according to the invention an image is picked up by converting a light image into a charge carrier image by means of the image sensor. The image pick-up apparatus is sensitive to electromagnetic radiation in a range covering ultraviolet radiation, visible light and infrared radiation. The image picked up is read-out from the image sensor so as to be converted into an electronic image signal which is suitable for supply to a monitor or to a buffer circuit while awaiting further image processing. In the image sensor light-sensitive elements are formed by applying an electric voltage to collecting gate electrodes with respect to isolating gate electrodes, which electric voltage has a polarity which opposes the polarity of the charge of the charge carriers to be collected. The collecting gate electrodes of a light-sensitive element are isolated in one or more directions by isolating gate electrodes whereto an electric voltage is applied, relative to the collecting gate electrodes, which is neutral or which has the polarity of the charge carriers to be collected. In another direction light-sensitive elements can be isolated from one another by isolating barriers which impede the diffusion of charge carriers in said other direction. Due to incident radiation charge carriers are released and collected in a region in the semiconductor body which extends mainly below the collecting gate electrodes and below the side of the isolator layer in the semiconductor, facing the semiconductor, in the depth direction of the light-sensitive elements. In as far as charge carriers are released by light incident at the area of an isolating gate electrode, the charge carriers are depleted partly to a substrate of the semiconductor body and are partly collected below adjacent collecting gate electrodes. A group of adjoining collecting gate electrodes defines a light-sensitive element and the active surface area of the light collection surface thereof is determined by the combined surface area of the adjoining gate electrodes. Several groups of adjoining gate electrodes can be formed and such groups define pixels of the charge carrier image to be formed by the image sensor. The spatial resolution is co-determined by the size of the pixels. By adjustment of electric voltages on gate electrodes, i.e. the gate voltages, the gate electrodes are adjusted so as to form collecting gate electrodes or isolating gate electrodes, the active surface area of respective light-sensitive elements thus being adjusted so that adjustability of the spatial resolution is achieved. The adjustability of the spatial resolution of the image sensor can be rendered dependent on a selected mode of operation of the image pick-up apparatus according to the invention, i.e. by connecting the control circuit to a control unit of the image pick-up apparatus. The control unit is arranged to select a mode of operation of the image pick-up apparatus.
A further preferred embodiment of an image pick-up apparatus according to the invention, in which the light-sensitive elements are arranged in rows and columns which constitute a matrix, is characterized in that the number of isolating gate electrodes between adjacent elements of a column of the matrix deviates from the number of isolating gate electrodes between adjacent elements of a row of the matrix.
In such an embodiment of an im
Bruijns Antonius J. C.
Dillen Bartholomeus G. M. H.
Ngo Ngan V.
U.S. Philips Corporation
Vodopia John F.
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