ASTM_F_617M_-_95.pdf

Designation:F 617M 95METRICStandard Test Method forMeasuring MOSFET Linear Threshold Voltage Metric1This standard is issued under the fixed designation F 617M;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers the measurement of MOSFET(see Note 1)linear threshold voltage under very low sweep rate ord-c conditions.It is a d-c conductance method applicable in the linear region of MOSFET operation where a drain voltage VDofapproximately 0.1 V is typical.NOTE1MOS is an acronym for metal-oxide semiconductor;FET is an acronym for field-effect transistor.1.2 This test method is applicable to both enhancement-mode and depletion-mode MOSFETs,and for both silicon-on-insulator(SOI)and bulk-silicon MOSFETs.The test method specifies positive voltage and current conventions specifically applicable ton-channel MOSFETs.The substitution of negative voltage and negative current make the test method directly applicable top-channel MOSFETs.1.3 This standard does not purport to address all of the safety concerns,if any,associated with its use.It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2.Terminology2.1 Definitions of Terms Specific to This Standard:2.1.1 drain-leakage currentof a MOSFET,the d-c current from the drain terminal when the gate voltage with respect to thethreshold voltage is such that the MOSFET is in the OFF state.2.1.2 threshold voltageof a MOSFET,for operation in the linear region,the gate-to-source voltage at which the drain currentis reduced to the leakage current.3.Summary of Test Method3.1 The drain-source current of the MOSFET under test is measured at several values of gate voltage for a fixed drain-sourcevoltage.A linear plot is made of the drain current as a function of gate voltage.The maximum tangent to the resulting curve isextrapolated to the gate-voltage axis or to the voltage independent line representing the drain-leakage current.This intercept is thethreshold voltage for the drain-source voltage and temperature conditions of the test.3.2 Before this test method can be implemented,test conditions appropriate for the MOSFET to be measured must be selectedand agreed upon by the parties to the test.Conditions will vary from one MOSFET type to another,and are determined in part bythe intended application.The following items are not specified by this test method,and shall be agreed upon between the partiesto the test:3.2.1 Reference temperature to which the measured threshold voltages shall be normalized.3.2.2 Permissible range of ambient temperature within which the measurement is to be conducted.The reference temperatureshall be within this range.NOTE2The temperature sensitivity of the threshold voltage may be as large as 5 mV/C,or more.The reproducibility of the measurements willbe degraded accordingly,unless the values of the threshold voltage are normalized to a common reference temperature.To reduce the effect thatuncertainties in the temperature sensitivity of the test devices will have on the reproducibility,no more than an appropriately small range of testtemperatures should be allowed.3.2.3 Drain voltage VDat which the measurement is to be made.3.2.4 Maximum drain current,IDM,maximum gate voltage,VGM,and gate voltage steps,DVG,over which the measurementis to be made.Values for IDM,VGM,and D VGshall be selected to permit taking enough data points to define adequately thedrain-current,gate-voltage characteristic curve in the region of the inflection point,namely,where the tangent to the curve has thelargest slope(maximum tangent).The value selected for DVGshall be one of the following:0.02,0.05,0.10,0.20,or 0.50 V.The1This test method is under the jurisdiction of ASTM Committee F-1 on Electronics and is the direct responsibility of Subcommittee F01.11 on Quality and HardnessAssurance.Current edition approved Nov.10,1995.Published January 1996.Originally published as F 617 79.Last previous edition F 617 91.1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.recommended procedure for selecting values for IDM,VGM,and DVGis provided in the Appendix.4.Significance and Use4.1 The threshold voltage is a basic MOSFET parameter that must be determined for the design and application of discreteMOSFETs and MOS(see Note 1)integrated circuits.Threshold voltage is utilized in circuit design to specify the turn-on voltageof MOSFETs,and thereby determine performance attributes such as speed,power,noise margin,etc.,of digital and analogcircuitry.4.2 The radiation-induced change in threshold voltage is a measure of ionizing radiation damage which results