Picturephone Silicon Target Signal Analysis

The silicon target, used as the image sensing element in the Picturephone® camera tube, 1-4 is composed of a matrix of diffused diodes. 921 922 T H E BELL SYSTEM TECHNICAL J O U R N A L , J U L Y - A U G U S T 1970 Signal characteristics of the target are the result of a complex interaction of the material and geometric parameters of the individual array diodes as well as the operating conditions of the target. We have analtyically investigated target signal characteristics by means of numerical computations, solving explicitly for depletion region geometry and capacitance and have determined signal characteristics as a function of Si-Si0 2 interface fixed charge density, sea resistance*, substrate resistivity, P + island geometry, Si0 2 -Si surface inversion phenomenon, and electron beam acceptance characteristics. Section II describes the diode array format and the basic relationship of signal current to array capacitance. The model of the reversed biased unit cell and the mathematic analysis are described in Sections II and III. Signal capabilities of a resistive sea diode array structure are discussed in Section IV and extended to include the effects of electron beam acceptance in Section V. An alternate geometric structure using conductive overlays is analyzed in Section VI. The relationship between the array dark current characteristic and target parameters is presented in Section VII. In the concluding section we present experimental verification of the model.