Date of Award

1975

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Electrical Engineering

Department

Electrical Engineering

First Advisor

Angaraih Ganesan Sadasiv

Abstract

16 x 16 element silicon image sensor arrays, utilizing the photodiode-bipolar transistor (PBT) element, were fabricated, tested and scanned in a television raster. Area arrays utilizing the PBT element are simple to fabricate requiring only two diffusions and one metallization. The spike noise cancellation scheme inherent in the PBT element was effectively utilized in the area arrays to reduce the peak value of the spike noise by more than an order of magnitude and to increase the peak value of the video signal.

The circuit analysis was performed using ECAP-1620. The photodiode was modeled by a non- linear capacitor and the transistor by a modified π-equivalent circuit. The variation of the base- emitter junction resistance and voltage drop with forward bias and the variation of the transistor gain with base current were included in the model. The effect of all the elements of the array on the video signals was taken into account. Very good agreement was obtained between the calculated and experimental results.

The collection process of the photogenerated charge in charge injection device (CID) image sensors was examined and a method is presented by which the collection efficiency can be calculated. Numerical techniques were utilized in the analysis. The method was applied to a specific epitaxial type structure. The contribution of the depleted and undepleted regions to the total collection efficiency of the sensor was calculated.

The relation between output signal charge and incident light intensity was also investigated. It is shown that the collection efficiency decreases with increasing signal charge and this results in non-linear transfer characteristics at high signal levels.

A design is presented for a CID type image sensor that can be operated in the back illumination mode. Except for the thinning step, the proposed structure is as simple to fabricate as present designs.

Calculations are also presented of the transmittance of Air/SiO2/Polysilicon/SiO2/Si structures in the spectral region between 0.4 and 1.0 μ m. It is shown that a judicious choice of the thicknesses of the oxide films, for a given polysilicon film thickness, can substantially increase the transmittance over a narrow wavelength band or over the entire wavelength region of interest here.

The dependence of the photocurent on the energy of the incident photons was investigated in silicon p-n junctions at room and higher temperatures for photon energies between 0.75 eV and 1.08 eV. he sensitivity of the method enabled high resolution measurement s in the absorption tail. At room temperature, thresholds were found at ~ 0.91 eV, 0.99 eV, and 1.026 eV. The derivative of the response showed extensive fine structure in this tail. The TO and LO phonon assisted transitions to the ground and excited s t ate of the exciton, reported by Shaklee and Nahory in the phonon emission region, were seen here with phonon absorption, occurring around 1.054 eV and 1.065 eV.

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