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Browse Prior Art Database

Capacitance Bridge for MOS Devices

IP.com Disclosure Number: IPCOM000082488D
Original Publication Date: 1974-Dec-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 46K

Publishing Venue

IBM

Related People

DeBar, DE: AUTHOR

Abstract

Described is a capacitance bridge employing a pulsed mode for measuring the capacitance of a metal-oxide semiconductor (MOS) device. The bridge circuit permits the measurement of capacitance versus voltage at 1 MHz with a voltage pulse width of less than 50 microseconds. Such information may be used to obtain a profile of silicon impurity distribution in ion implanted MOS devices.

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Capacitance Bridge for MOS Devices

Described is a capacitance bridge employing a pulsed mode for measuring the capacitance of a metal-oxide semiconductor (MOS) device. The bridge circuit permits the measurement of capacitance versus voltage at 1 MHz with a voltage pulse width of less than 50 microseconds. Such information may be used to obtain a profile of silicon impurity distribution in ion implanted MOS devices.

Fig. 1 shows the system environment for the capacitance bridge.

The sine-wave generator 1 generates a subharmonic frequency of 1 MHz which is output on line 9 to the bridge 4. A sink pulse from the sine-wave generator 1 triggers the sampling oscilloscope 2. The sampling oscilloscope 2 generates a trigger pulse to the pulse generator 3. The pulse generator 3 outputs a 50 microsecond square-wave pulse to the bridge 4 over line 8. A DC bias potential is supplied to the bridge 4 over line 10.

A more detailed illustration of the capacitance bridge is shown in Fig. 2. The 50 microsecond pulse on line 8, the sine-wave on line 9, and the DC potential on line 10 are added together by the operational amplifier A1. A mirror image 180 degree phase shift is executed by operational amplifier A2 having an input connected to the output of operational amplifier A1. Operation amplifier A3 provides an identical time delay to that imposed by amplifier A2, while providing a unity gain at 0 degree phase shift.

The noninverted composite waveform is output from operational am...