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Automatic Threshold Voltage Monitor for Stressed FET Devices

IP.com Disclosure Number: IPCOM000077429D
Original Publication Date: 1972-Jul-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 46K

Publishing Venue

IBM

Related People

Carlos, A: AUTHOR [+2]

Abstract

The time-consuming manual threshold voltage V(T) measuring technique, based on the measurements of two saturation drain currents is replaced by an automatic monitor, whose operation is based on the measurement of a single saturation current: V(T) = V(G) - A square of I(D). Here V(G) (gate voltage) is kept constant and A is a calibration constant, depending on the transconductance and the geometry of the field-effect transistor (FET) device: (Image Omitted) Since V(T) is time dependent and a function of stress conditions, the threshold voltage change delta V(T) will be: (Image Omitted)

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Automatic Threshold Voltage Monitor for Stressed FET Devices

The time-consuming manual threshold voltage V(T) measuring technique, based on the measurements of two saturation drain currents is replaced by an automatic monitor, whose operation is based on the measurement of a single saturation current: V(T) = V(G) - A square of I(D). Here V(G) (gate voltage) is kept constant and A is a calibration constant, depending on the transconductance and the geometry of the field-effect transistor (FET) device:

(Image Omitted)

Since V(T) is time dependent and a function of stress conditions, the threshold voltage change delta V(T) will be:

(Image Omitted)

The figure shows the block diagram of one automatic monitor built for the purpose of recording the delta V(T) of six stressed FET devices. In this particular apparatus six N-channel devices are placed into three stress ovens (each at a different temperature), and are biased in the standard stress configuration wherein the source, drain and substrate are interconnected and maintained at a predetermined voltage, while the gate voltage is varied.

Every hour (or any other time between 15 minutes and 24 hours), regulated by pulses from a 24-hour clock, the FET devices are sequentially (at three- minute intervals) switched from the standard stress configuration to the CN readout configuration. The dwelling time in the readout and recording period is ten seconds.

The actual switching from the standard to the ON configuration is carried out by a series of six triple-me...