FR2687846A1 - Image detection apparatus - Google Patents

Abstract

The invention relates to image detection techniques. A reliable and relatively economical means for obtaining a rapid response in an image detection apparatus with a charge-coupled semiconductor device consists in incorporating in the apparatus a radioactive light source in order to illuminate the charge-coupled material, to an extent sufficient to polarise it to a "bald zero" in the case of a charge-coupled device with a surface channel, or to a "light-faced zero" in the case of a charge-coupled device with a buried channel. Application to detection systems.

Description

-2687846

  Its present invention relates to the use of semiconductor devices for the detection of an image.

  A charge coupled device (DCC) is an integrated circuit device that works by transferring charge "packets" into the device under the influence of electric fields. These charge packets can be created electrically or optically and can be used to represent

  inside the device an external signal applied to the device

  positive, for example an image formed on the device by electromagnetic radiation.

  In a device of the silicon-silicon dioxide type, the charge packets exist in a layer of silicon.

  pletion at the border between a layer of silicon dioxide and a layer of silicon In a surface channel device, the depletion layer is on the surface of the device, but in a buried channel device it is slightly at the - below the surface. In a surface channel DCC, there are "fast surface states" which empty themselves of any charge if the DCC has not received an input signal for a certain time. If a signal is then applied, these "states "fill up from the charge packet and then slowly re-emit this trapped charge when the input signal is sup-25 awarded If the admissible time for charge transfer is short vis-à-vis the time constant from this re-transmission, the degradation of the signal becomes significant. In the field of surface channel DCC fast image sensors, it has previously been proposed to minimize this degradation of the signal by illumination of the device in order to constantly maintain the fast surface states in the full state, which allows transfer fast signal charge packet, without disturbance The charge produced by this background illumination is "zero fat", and is typically 10 to 50% of the charge capacity

2 of the device.

  A similar effect occurs in a buried channel charge coupled device (DCC). The defects of the crystal lattice which cause the trapping of charges in solid silicon are less numerous in this case and a background level corresponding to 2 at only 10% of the maximum load capacity (what is called a "zero lean") is necessary to allow a transfer without disturbance of the signal charge packets It is noted that the need10 to use background illumination to produce a "skinny zero" is less common than the need to produce a

  "zero grast 'in a surface channel DCC.

  The term "reinforced zero" is used here to denote a "bold zero" when the DCC is of the channel type.

  surface, and a "skinny zero" -when the DCC is of the buried channel type.

  Various different light sources have been proposed previously to illuminate an image detector with

  DCC with surface channel An example of a light source20 consists of a light-emitting diode the applicant has examined the proposals made previously for sources

  these bright in DCC and found that they were not satisfactory One problem is that these sources are large and unreliable, and another problem is that they are relatively expensive A goal of the The invention is to provide a fast, reliable, and relatively inexpensive DCC image detector. The invention provides an image detection apparatus for detecting the presence in a field of a radio transmitter.

  electromagnetic radiation having a characteristic wavelength, this apparatus comprising a semiconductor device

  charge transfer sensor which is sensitive to this radiation and is capable of producing a useful output signal, and which is characterized by: a narrow band optical filter which strongly attenuates all wavelengths except 1

  3 those contained in a narrow band which includes the long

  characteristic wavelength; and a source which, by a radioactive decay mechanism, emits radiation of a wavelength to which the charge transfer device 5 is sensitive, the source being placed in such a way that the radiation which 'it emits falls on the charge transfer device and polarizes it at least to a "reinforced zero", as low as the intensity falling on the charge transfer device which corresponds to

  background radiation filtered by the filter.

  The Applicant has determined that if the level of illumination of an internal background illumination device of an image detection apparatus is set for a dark background outside of the apparatus (such as for example in the case of night operation with the sky as background), when the device is used with luminous external backgrounds (for example a clear sky or a sunny ground), the background intensity tota 2 e which falls on the image detector at DCC, which

  is the sum of the internal background level produced by the preset light source and the external background level, is greater than the critical level, which means that the response time

  DCC may in these circumstances be increased to the point of becoming marginal. However, the possible disadvantage of having a

  fixed intensity light source will probably be more than compensated in certain applications by the excellent reliability

  lity, reduced cost and size and ease of manufacture to obtain any desired shape, which are associated with radioactive light sources.30 It goes without saying that many modifications can

  can be made to the device described and shown, without

depart from the scope of the invention.

REVEYIDICATIQNS

  1 Image detection apparatus, intended to detect the presence in a field of an emitter of electromagnetic radiation of a characteristic wavelength and comprising a semiconductor charge transfer device which is sensitive to this radiation and which is capable of providing a useful output signal, characterized in that it further comprises a source of radioactive decay radiation, of a wavelength to which the charge transfer device10 is sensitive, in the purpose of illuminating the semiconductor device O 2 Apparatus according to claim 1, characterized in that the radioactive decay source produces a

  radiation of sufficient intensity to polarize the semiconductor device to a "reinforced zero", in the sense defined previously for this term.

  3 Apparatus according to claim 2, characterized in that the semiconductor device is a surface channel charge coupled device. 20 4 Apparatus according to claim 2, characterized in that the semiconductor device is a channel charge coupled device. 5 buried apparatus according to claim 1, characterized in that it comprises a narrow band optical filter which, in the radiation of the emitter, preferentially lets through only the radiation which has a wavelength

  included in the narrow band of the filter.

FRENCH REPUBLIC

  NATIONAL INSTITUTE OF INDUSTRIAL PROPERTY

  Erratum Patent n A 1 Patent application n 84 06 208 Publication N: 2 687 846 International classification: CLASST 5

HOIL 12/31.

& C "'O

  26 bis, rue de Saint-Pétersbourg 75800 Paris Cédex 08 Té: (1) 42 94 52 52 Telex: IN Pl PARIS Fax: (t 1) 42 93 59 30 National public establishment created by facade P 5 I-444 of April 19 1951 s .;

ERRATUM

  In section 30 of the cover page of the specification of the patent application:

I should read: 20 08 82 GB 8224004.

  In section 60 of the same cover page: You should read: Transformation of the European patent application n 83304809 3 filed on 19 8 83 The date indicated in 22 is that of the transformation (chap III of decree n 78 1011 of 10 October 1978)

-8 SEP 1993

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