Abstract: Isolation between the heavily-doped active regions of an active pixel sensor cell is provided by utilizing a series of isolation regions which have a doping concentration that is approximately equal to the doping concentration of a low-density drain (LDD) region. A first isolation region of the series, which has the same conductivity type as the active regions, is formed to adjoin a first active region. A second isolation region of the series, which has the opposite conductivity type as the active regions, is formed to adjoin the first isolation region. A third isolation region, which has the same conductivity type as the active regions, is formed to adjoin the second isolation region and a second active region.

Abstract: The stress placed on the silicon lattice of a photodiode during the formation of field oxide regions by the local oxidation of silicon (LOCOS) is eliminated in the present invention by utilizing a negatively-charged layer of polysilicon to isolate the implanted n-type region of the photodiode from the implanted regions of adjacent photodiodes or other devices. In addition, stress is further reduced in the present invention by forming the n-type region of the photodiode with phosphorous, and by lowering the dose such that the n-type region is lightly doped.

Abstract: The leakage current at the silicon-to-silicon dioxide interfaces of an active pixel sensor cell is substantially reduced by eliminating field oxide from the cell, and by insuring that, during integration, every surface region of the cell that is not heavily doped is either biased into accumulation or biased into inversion. Each of these states, in turn, substantially limits the number of electrons from thermally-generated electron-hole pairs at the surface that can contribute to the leakage current.

Abstract: A CMOS circuit formed in a silicon-on-insulator (SOI) substrate includes MOSFETs having drain and body diffusions which extend through the silicon layer to the surface of the insulating layer. Each of drains of the N-channel and P-channel MOSFETs serves also as a terminal (anode or cathode) of a diode that is connected in series with the MOSFET. This structure allows the CMOS device to be fabricated as a completely symmetrical structure without adding processing steps beyond those customary in fabricating conventional CMOS devices.

Abstract: The quantum efficiency of a photodiode is substantially increased by forming the photodiode on a heavily-doped layer of semiconductor material which, in turn, is formed on a semiconductor substrate. The heavily-doped layer of semiconductor material tends to repel information carriers in the photodiode from being lost to the substrate, and prevents noise carriers from the substrate from diffusing up into the photodiode. In addition, the red and blue photoresponses are balanced by adjusting the depth of the photodiode.

Abstract: The accuracy of an active pixel sensor cell is increased by utilizing a reset diode in lieu of the reset transistor that is conventionally used to reset the voltage on the photodiode of the cell. The reset diode, which is largely unaffected by 1/f noise, consistently resets the photodiode to a substantially constant voltage as opposed to the reset transistor which varies the reset voltage on the photodiode across integration periods due to the effect of 1/f noise. In the present invention, the photodiode is formed by forming a well region of a second conductivity type in a substrate of a first conductivity type. The reset diode is then formed by forming a reset region of the first conductivity type in the well region.

Abstract: The amount of silicon real estate consumed by a photodiode-based active pixel sensor cell is reduced by utilizing a parasitic transistor to reset the voltage on the photodiode in lieu of the conventional use of a reset transistor. The parasitic transistor is formed by forming a doped region a distance apart from the well region of the photodiode, which defines a parasitic channel region therebetween, and a reset gate over the parasitic channel region.

Abstract: A preferred pnp bipolar phototransistor pixel element in accordance with the present invention has a p-type collector region formed in p-type semiconductor material. An n-type base region is formed in the collector region. A p-type emitter region is formed in the base region. An annular n-type capacitor region is formed in the base region surrounding and spaced-apart from the emitter region. Conductive material is disposed over the capacitor region and separated therefrom by underlying dielectric material to define the pixel element's coupling capacitor.