ASTM_F_769_-_00.pdf

Designation:F 769 00Standard Test Method forMeasuring Transistor and Diode Leakage Currents1This standard is issued under the fixed designation F 769;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 leakagecurrents of transistors and diodes.Electronic devices exposedto ionizing radiation may show increases in leakage current asthe accumlated total dose rises.1.2 These procedures are intended for the measurement ofcurrents in the range from 1011to 103A.1.3 This test method may be used with either a virtual-ground current meter or a resistance-shunt current meter.1.4 The values stated in Internationl System of Units(SI)are to be regarded as standard.No other units of measurementare included in this test method.1.5 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Terminology2.1 Definitions:2.1.1 resistance-shunt metera meter that determines cur-rent by measuring the voltage generated across shunt resistorsby the current.2.1.2 virtual-ground metera meter employing feedback tothe amplifier in such a way as to make the meter input appearto be at ground potential.3.Summary of Test Method3.1 Ajunction whose leakage is to be determined is reverse-biased with a power supply.A current meter is placed in serieswith the junction and the appropriate range is selected on themeter.The current is read directly from the meter readout.4.Significance and Use4.1 Knowledge of diode and transistor leakage currents isvery important to the circuit designer.Proper transistor biasingdepends on accurate leakage current data.4.2 Ionizing radiation,that is,space radiation or gammaradiation,may have a long term(permanent)effect on theleakage current.Thus,the total dose to which a transistor ordiode has been exposed may have a significant effect on theleakage current and hence the biasing and power supplystagility and functioning.This must be considered duringdesign,device selection and production line part device accep-tance.5.Interferences5.1 Noise generated by thermal agitation in the variousresistances in the test circuit sets an ultimate limit of instrumentresolution.The noise current generated in a current meter shuntresistor is proportional to the inverse square root of theresistance,so a high shunt resistance value is desirable.5.2 Other sources of noise are ac signals propagatingthrough the power supply or imposed on the test leads.Ameterwith a high ac rejection ratio and with high common moderejection ratio will be less sensitive to such forms of noise.Ashielded test fixture may be required for proper measurementof low currents.5.3 All components associated with very high resistancecircuitry should be mechanically rigid.Movement of a coaxialcable can produce piezoelectric and triboelectric effects in thecable which result in voltages across the current meter inputs.5.4 When working with a high resistance source,all leakagepaths must be high in comparison to the circuit resistance.Phenolic or rubber insulation,for example,may have aresistance of only 109V,causing large errors in measurementswith circuit resistances of greater than 108V.5.5 Circuits employing a feedback picoammeter can havemeasurement errors which result from offset current,offsetvoltage,drift,and time constants in the amplifier.Amplifiertime constants are of particular importance whenever theannealing rate of an irradiated device approaches the samplingrate of the current meter.5.6 The voltage drop across a resistance-shunt type ammeterfor a given current varies with the range selected.Therefore,arange which gives maximum meter resolution will also intro-duce maximum voltage drop error.An excellent way ofdetermining the input resistance of an ammeter is by directmeasurement using a transistor curve tracer.A range should beselected which has an associated resistance less than 1%of theequivalent resistance(bias voltage/leakage current)of the testdevice.5.7 Care must be taken to keep the test device and testfixture free from contamination such as dust,dirt,solder flux,1This test method is under the jurisdiction of ASTM Committee F-1 onElectronicsand is the direct responsibility of Subcommittee F01.11 on Quality andHardness Assurance.Current edition approved June 10,2000.Published August 2000.Originallypublished as F 769 82.Last previous edition F 769 95.1Copyright ASTM,100 Barr Harbor Drive,West Conshohocken,PA 19428-2959,United States.oil films,fingerprints,and water vapor.It is therefore importantto perform this measurement in a clean,dry envir