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# Direct Reading Ideality Factor Meter

IP.com Disclosure Number: IPCOM000044262D
Original Publication Date: 1984-Nov-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 2 page(s) / 22K

IBM

## Related People

Hsieh, CM: AUTHOR [+3]

## Abstract

The Schottky barrier diode (SBD) current-voltage characteristics are expressed by the following function: qV __ I = Is ( e hKT - 1 ) where V = voltage Is= the saturation current q = the electronic charge K = Boltzmann's constant T = absolute temperature h = the ideality factor A known technique for evaluating h is to obtain many data points and fit the above equation by a logarithmic transformation. Utilizing the small signal characteristics of the SBD the disclosed circuit may be directly employed to measure the ideality factor h. The DC operating current is set by VDC and RL . Superimposed on the DC current is the AC current set by VAC and R1 . By proper choice of DC current the AC voltmeter will read the ideality factor h directly.

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Direct Reading Ideality Factor Meter

The Schottky barrier diode (SBD) current-voltage characteristics are expressed by the following function: qV __ I = Is ( e hKT - 1 ) where V = voltage Is= the saturation current q = the electronic charge K = Boltzmann's constant T = absolute temperature h = the ideality factor A known technique for evaluating h is to obtain many data points and fit the above equation by a logarithmic transformation. Utilizing the small signal characteristics of the SBD the disclosed circuit may be directly employed to measure the ideality factor h. The DC operating current is set by VDC and RL . Superimposed on the DC current is the AC current set by VAC and R1 . By proper choice of DC current the AC voltmeter will read the ideality factor h directly. The AC characteristic is qV __ dI/dV = q/hKT Is e hKT = q/hKT IDC if V>>3KT/q (NN75 mv @ 25OEC) Since KT/q is about 25.9 mV at 25OEC, an operating current (DC) of 2.59 mA will permit direct reading of the ideality factor. Also at this current (2.59 mA), the small signal resistance of the diode is about 10 KL and the indicated ideality factor will be insignificantly affected by series resistance. Calibration is set by inserting a 10 KL resistor in place of the diode and adjusting the AC current for unity output. Amplification of the output and conversion to DC is possible. This will permit a true small signal measurement.

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