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EP0399601A1
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Dark current reduction in buried channel charge coupled imaging device
Assignee: Koninklijke Philips NV
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Filing: 1990-05-17
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Granted: —
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Expires: 2010-05-17
Abstract
Abstract In CCD's, the major part of the dark current is caused by surface states. This dark current is disturbing, especially in image sensors, because the sensitivity of the camera is limited thereby. When according to the invention the integrating gates are varied periodically, the subjacent surface parts of the - buried - channel being brought periodically into inversion and into depletion, whilst maintaining the charge-containing capacity, a considerable reduction of the dark current can be obtained. In image sensors, voltage variation preferably occurs during the fly-back time (Tl).
Inventors
- 👤 Michael Alwin William Stekelenburg
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-09 18:31
CPC Classifications
H; H10; H10F; H10F39/00; H10F39/10; H10F39/12; H10F39/15; H10F39/153; H10F39/158; H04; H04N; H04N25/00; H04N25/60; H04N25/63; H04N25/70; H04N25/71
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
179 words
A charge-coupled device of the buried channel type comprising a semiconductor body having a charge transport channel of the one conductivity type, which is located near a surface and passes via a pn junction into an adjoining layer of the second conductivity type opposite to the first conductivity type, the surface being provided with a series of successive electrodes, which are separated by an isolating layer from the surface and are connected to a voltage source for applying clock voltages having a blocking level and an active level, while in the charge transport channel a potential barrier or a potential well is induced, the blocking level being chosen so that inversion of the conductivity type occurs at the surface of the semiconductor body, characterized in that the active level is chosen so that depletion occurs only at the surface, while during operation the surface parts of the charge transport channel corresponding to at least a part of the said electrodes are brought alternately into depletion, in which event signal charge can be stored below the electrodes, and into inversion.
Claim 2
Dependent Claim
179 words
A charge-coupled device of the buried channel type comprising a semiconductor body having a charge transport channel of the one conductivity type, which is located near a surface and passes via a pn junction into an adjoining layer of the second conductivity type opposite to the first conductivity type, the surface being provided with a series of successive electrodes, which are separated by an isolating layer from the surface and are connected to a voltage source for applying clock voltages having a blocking level and an active level, while in the charge transport channel a potential barrier or a potential well is induced, the blocking level being chosen so that inversion of the conductivity type occurs at the surface of the semiconductor body, characterized in that the active level is chosen so that depletion occurs only at the surface, while during operation the surface parts of the charge transport channel corresponding to at least a part of the said electrodes are brought alternately into depletion, in which event signal charge can be stored below the electrodes, and into inversion.
Claim 3
Dependent Claim
112 words
A charge-coupled device as claimed in Claim 1, characterized in that the electrodes comprise at least a group of n+1 successive electrodes with n > 3, which together define a charge storage site in the charge transport channel, and in that the voltage source supplies during a period in which a charge packet is stored in said storage site the blocking level to the two outer electrodes of these n+1 electrodes and alternating voltages varying during the charge storage period between the blocking level and the active level to the electrodes located between these outer electrodes so that the surface parts below these electrodes are alternately brought into inversion and into depletion.
Claim 4
Dependent Claim
81 words
A charge-coupled device as claimed in Claim 2, characterized in that the charge transport channel with the associated channels forms part of an image sensor arrangement having a system of image sensor elements arranged in lines and columns and a system of transport channels, which extend in the column direction and via which charge packets generated by absorption of radiation can be transported in the column direction to means with the aid of which the charge packets are read out linewise.
Claim 5
Dependent Claim
57 words
A charge-coupled device as claimed in Claim 3, characterized in that in the period in which a charge packet is stored in the said storage site the voltages at the inner electrodes of said storage site are periodically varied in the period coinciding with the line fly-back time lying between steps of reading out two successive lines.
Claim 6
Dependent Claim
83 words
A charge-coupled device as claimed in Claim 4, characterized in that during the line fly-back time the number of the inner electrodes to which the active voltage level is applied is at least temporarily lower than in the period between two line fly-back times, as a result of which the surface of the potential well is reduced temporarily, and in that draining means are provided, via which with this reduction of the potential well any excess quantity of charge carriers can be drained.
Claim 7
Dependent Claim
17 words
A camera comprising an image sensor arrangement as claimed in any one of Claims 3 to 5.
References Cited (Backward Citations)
EP0247503A2
Cited
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