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Automatic Capacitance Voltage Measurement Technique

IP.com Disclosure Number: IPCOM000086397D
Original Publication Date: 1976-Sep-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 32K

Publishing Venue

IBM

Related People

El-Kareh, B: AUTHOR [+2]

Abstract

This is a system for automatic measurement of the capacitance of a metal insulator semiconductor as a function of applied voltage, which is provided at output terminal 13. The system can be utilized to make fast accurate measurements over a wide range of frequencies, to readily calculate such parameters as the flat band voltage, the instantaneous minimum capacitance and its time dependence for the assessment of semiconductor surface quality, the inverse square capacitance for the evaluation of the doping profile of the semiconductor, the low frequency capacitance voltage traces to evaluate surface state density, and the stress induced shifts of the flat band voltage for reliability purposes.

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Automatic Capacitance Voltage Measurement Technique

This is a system for automatic measurement of the capacitance of a metal insulator semiconductor as a function of applied voltage, which is provided at output terminal 13. The system can be utilized to make fast accurate measurements over a wide range of frequencies, to readily calculate such parameters as the flat band voltage, the instantaneous minimum capacitance and its time dependence for the assessment of semiconductor surface quality, the inverse square capacitance for the evaluation of the doping profile of the semiconductor, the low frequency capacitance voltage traces to evaluate surface state density, and the stress induced shifts of the flat band voltage for reliability purposes.

The device under test is depicted by the variable capacitor Co which is in parallel with the fixed, distributed capacitance Cd. The desired DC voltage can be applied directly by the digital-analog converter (DAC) and switch S. The AC signal is fed from the generator 10 through the calibrating capacitance Cc, in series with Co + Cd. The DC and AC voltages are sensed with the voltage sensing probe 11. Cout couples the AC portion of the signal appearing at terminal 1 to the operational amplifiers OP1 and OP2. OP1 provides a buffering action and gain for the AC signal, which is provided at terminal 2. OP2 acts as a differential amplifier, sensing the AC generator voltage amplitude and subtracting the AC voltage component at terminal 1. The resulting voltage may be amplified and provided at terminal 3. The current through Cc is then proportional to the voltage at terminal 3.

The value of the calibrated capacitance Cc is chosen low when compared to the capaci...