1、Designation: F 448 99 (Reapproved 2005)Standard Test Method forMeasuring Steady-State Primary Photocurrent1This standard is issued under the fixed designation F 448; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、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 steady-stateprimary photocurrent, Ipp, generated in semiconductor deviceswhen t
3、hese devices are exposed to ionizing radiation. Theseprocedures are intended for the measurement of photocurrentsgreater than 109As/Gy(Si or Ge), in cases for which therelaxation time of the device being measured is less than 25 %of the pulse width of the ionizing source. The validity of theseproced
4、ures for ionizing dose rates as great as 108Gy(Si or Ge)/shas been established. The procedures may be used for mea-surements at dose rates as great as 1010Gy(Si or Ge)/s;however, extra care must be taken.Above 108Gy/s the packageresponse may dominate the device response for technologiessuch as compl
5、ementary metal-oxide semiconductor, (CMOS)/silicon-on sapphire (SOS). Additional precautions are alsorequired when measuring photocurrents of 109As/Gy(Si orGe) or lower.1.2 Setup, calibration, and test circuit evaluation proceduresare also included in this test method.1.3 Because of the variability
6、between device types and inthe requirements of different applications, the dose rate rangeover which any specific test is to be conducted is not given inthis test method but must be specified separately.1.4 The values stated in International System of Units (SI)are to be regarded as standard. No oth
7、er units of measurementare included in this standard.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 o
8、f regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E 668 Practice for theApplication of Thermoluminescence-Dosimetry (TLD) Systems for DeterminingAbsorbed Dosein Radiation-Hardness Testing of Electronic DevicesF 526 Test Method for Measuring Dose for Use in LinearAccele
9、rator Pulsed Radiation Effects Tests3. Terminology3.1 Definitions:3.1.1 fall time, nthe time required for a signal pulse todrop from 90 to 10 % of its steady-state value.3.1.2 primary photocurrent, nthe flow of excess chargecarriers across a p-n junction due to ionizing radiation creatingelectron-ho
10、le pairs throughout the device. The charges associ-ated with this current are only those produced in the junctiondepletion region and in the bulk semiconductor materialapproximately one diffusion length on either side of thedepletion region (or to the end of the semiconductor material,whichever is s
11、horter).3.1.3 pulse width, nthe time a pulse-amplitude remainsabove 50 % of its maximum value.3.1.4 rise time, nthe time required for a signal pulse torise from 10 to 90 % of its steady-state value.4. Summary of Test Method4.1 In this test method, the test device is irradiated in theprimary electron
12、 beam of a linear accelerator. Both the irradia-tion pulse and junction current (Fig. 1) are displayed andrecorded. Placement of a thin, low atomic number (Z#13)scattering plate in the beam is recommended to improve beamuniformity; the consequences of the use of a scattering platerelating to interfe
13、rence from secondary electrons are described.The total dose is measured by an auxiliary dosimeter. Thesteady-state values of the dose rate and junction current and therelaxation time of the junction current are determined from thedata trace and total dose.4.2 In special cases, these parameters may b
14、e measured at asingle dose rate under one bias condition if the test is designedto generate information for such a narrow application. Thepreferred approach, described in this test method, is to char-acterize the radiation response of a device in a way that isuseful to many different applications. F
15、or this purpose, theresponse to pulses at a number of different dose rates isrequired. Because of the bias dependence of the depletion1This test method is under the jurisdiction of ASTM Committee F01 onElectronics and is the direct responsibility of Subcommittee F01.11 on Quality andHardness Assuran
16、ce.Current edition approved Jan. 1, 2005. Published January 2005. Originallyapproved in 1975 as F 448 75 T. Last previous edition approved in 1999 asF 448 99.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of A
17、STMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.volume, it is possible that more than one bias level will berequired during the photocur
18、rent measurements.5. Significance and Use5.1 The steady-state photocurrent of a simple p-n junctiondiode is a directly measurable quantity that can be directlyrelated to device response over a wide range of ionizingradiation. For more complex devices the junction photocurrentmay not be directly rela
19、ted to device response.5.2 Zener Diode In this device, the effect of the photo-current on the Zener voltage rather than the photocurrent itselfis usually most important. The device is most appropriatelytested while biased in the Zener region. In testing Zener diodesor precision voltage regulators, e
20、xtra precaution must be takento make certain the photocurrent generated in the device duringirradiations does not cause the voltage across the device tochange during the test.5.3 Bipolar TransistorAs device geometries dictate thatphotocurrent from the base-collector junction be much greaterthan curr
21、ent from the base-emitter junction, measurements areusually made only on the collector-base junction with emitteropen; however, sometimes, to obtain data for computer-aidedcircuit analysis, the emitter-base junction photocurrent is alsomeasured.5.4 Junction Field-Effect DeviceA proper photocurrentme
22、asurement requires that the source be shorted (dc) to thedrain during measurement of the gate-channel photocurrent. Intetrode-connected devices, the two gate-channel junctionsshould be monitored separately.5.5 Insulated Gate Field-Effect DeviceIn this type ofdevice, the true photocurrent is between
23、the substrate and thechannel, source, and drain regions. A current which cangenerate voltage that will turn on the device may be measuredby the technique used here, but it is due to induced conduc-tivity in the gate insulator and thus is not a junction photocur-rent.6. Interferences6.1 Air Ionizatio
24、n A spurious component of the currentmeasured during a photocurrent test can result from conductionthrough air ionized by the irradiation pulse.Although this is notlikely to be a serious problem for photocurrents greater than109As/Gy(Si or Ge), the spurious contribution can easily bechecked by measu
25、ring the current while irradiating the testfixture in the absence of a test device. Air ionization contribu-tions to the observed signal are proportional to applied field,while those due to secondary emission effects (see 6.2) are not.The effects of air ionization external to the device may beminimi
26、zed by coating exposed leads with a thick layer ofparaffin, silicone rubber, or nonconductive enamel or bymaking the measurement in vacuum.6.2 Secondary Emission3Another spurious component ofthe measured current can result from charge emission from, orcharge injection into, the test device and test
27、circuit. This maybe minimized by shielding the surrounding circuitry andirradiating only the minimum area necessary to ensure irradia-tion of the test device. Reasonable estimates of the magnitudeto be expected of current resulting from secondary-emissioneffects can be made based on the area of meta
28、llic targetmaterials irradiated. Values generally range between 1011and109As/cm2Gy, but the use of a scatter plate with an intensebeam may increase this current.6.3 Orientation The effective dose to a semiconductorjunction can be altered by changing the orientation of the testunit with respect to th
29、e irradiating electron beam. Mosttransistors and diodes may be considered “thin samples (interms of the range of the irradiating electrons). However,high-power devices may have mounting studs or thick-walledcases that can act to scatter the incident beam, thereby reducingthe dose received by the sem
30、iconductor chip. Care must betaken in the mounting of such devices.6.4 BiasAs the effective volume for the generation ofphotocurrent in p-n junction devices includes the space-chargeregion, Ippmay be dependent on applied voltage. As appliedvoltages approach the breakdown voltage, Ippincreases sharpl
31、ydue to avalanche multiplication. If the application of the testdevice is known, actual bias values should be used in the test.If the application is not known, follow the methods forchecking the bias dependence given in Section 10.6.5 Nonlinearity Nonlinearities in photocurrent responseresult from s
32、aturation effects, injection level effects on life-times, and, in the case of bipolar transistors, a lateral biasing3Sawyer, J. A., and van Lint, V. A. J., “Calculations of High-Energy SecondaryElectron Emission,” Journal of Applied Physics, JAPIA, Vol 35, No 6, June 1964,pp. 17061711.FIG. 1 Ionizat
33、ion Radiation Pulse and Typical Primary Photocurrent ResponseF 448 99 (2005)2effect which introduces a component of secondary photocur-rent into the primary photocurrent measurement.4For thesereasons, photocurrent measurements must generally be madeover a wide range of dose rates.6.6 Electrical Nois
34、e Since linear accelerator facilities areinherent sources of r-f electrical noise, good noise-minimizingtechniques such as single-point ground, filtered dc supply lines,etc., must be used in photocurrent measurements.6.7 Temperature Device characteristics are dependent onjunction temperature; hence,
35、 the temperature of the test shouldbe controlled. Unless otherwise agreed upon by the parties tothe test, measurements will be made at room temperature (236 5C).6.8 Beam Homogeneity and Pulse-to-Pulse RepeatabilityThe intensity of a beam from a linear accelerator is likely tovary across its cross se
36、ction. Since the pulse-shape monitor isplaced at a different location from the device under test, themeasured dose rate may be different from the dose rate towhich the device was exposed. The spatial distribution andintensity of the beam may also vary from pulse to pulse. Thebeam homogeneity and pul
37、se-to-pulse repeatability associatedwith a particular linear accelerator should be established by athorough characterization of its electron beam prior to perform-ing a photocurrent measurement.6.9 Ionizing Dose Each pulse of the linear acceleratorimparts a dose of radiation to both the device under
38、 test and thedevice used for dosimetry. The ionizing dose deposited in asemiconductor device can change its operating characteristics.As a result, the photocurrent that is measured after severalpulses may be different from the photocurrent that is charac-teristic of an unirradiated device. Care shou
39、ld be exercised toensure that the ionizing dose delivered to the device under testis as low as possible consistent with the requirements for agiven dose rate and steady-state conditions. Generally, this isdone by minimizing the number of pulses the device receives.The dose must not exceed 10 % of th
40、e failure dose for thedevice.6.10 The test must be considered destructive if the photo-current exceeds the manufacturers absolute limit.7. Apparatus7.1 Regulated dc Power Supply, with floating output toproduce the voltages required to bias the junction.7.2 Oscilloscopes Either a single dual-beam, or
41、 twosingle-beam oscilloscopes that have adequate bandwidth capa-bility of both main frames and plug-ins to ensure that radiationresponse and peak steady-state values are accurately displayed.7.2.1 Oscilloscope Camera(s) and Film, capable of record-ing single transient traces at a sweep rate consiste
42、nt with goodresolution at the pulse widths used in the test.7.3 Digitizers with Bandwidth, Sampling Interval, andTime-base Capabilities, adequate for handling the transientsignals with good resolution for all pulse widths utilized in thetest may be used. Hard copy printouts of the recorded signalmay
43、 be a part of the capability of this apparatus.7.4 Cabling, to complete adequately the connection of thetest circuit in the exposure area with the power supply andoscilloscopes in the data area. Any type of ungrounded wiringmay be used to connect the power supply to the bias points ofthe test circui
44、t; however, coaxial cables properly terminated atthe oscilloscope input are required for the signal leads.7.5 Test Circuits One of the following test circuits:7.5.1 Resistor-Sampling Circuit (Fig. 2)For most tests,the configuration of Fig. 2(a) is appropriate. The resistors R2serve as high-frequency
45、 isolation and must be at least 20 V.The capacitor C supplies the charge during the current tran-sient; its value must be large enough that the decrease involtage during a current pulse is less than 10 %. Capacitor Cshould be paralleled by a small (approximately 0.01 F)low-inductance capacitor to en
46、sure that possible inductiveeffects of the large capacitor are offset. The resistor R0is toprovide the proper termination (within 62 %) for the coaxialcable used for the signal lead. When the photocurrents arelarge, it is necessary to use a small-value resistor, R1, in theconfiguration of Fig. 2(b)
47、to keep the signal small so as tomaintain the bias across the junction within 10 % of itsnominal value during the test. The response characteristics ofthis circuit must be adequate to ensure that the current signal isaccurately displayed (see 9.4).7.5.2 Current Transformer Circuit (Fig. 3)In this ci
48、rcuit,R2and C have the same significance as in the resistor-samplingcircuit, but it may be required that the signal cable monitoringthe current transformer be matched to the characteristic imped-ance of the transformer, in which case R0would have thisimpedance (within 62 %), which is specified by th
49、e manufac-turer of the current transformer. The current transformer musthave a bandwidth sufficient to ensure that the current signal isaccurately displayed. Rise time must be less than 10 % of thepulse width of the radiation pulse being used. The lowfrequency cutoff of some commercial current transformers issuch that significant droop may occur for pulse widths greaterthan 1 s. Do not use a transformer for which this droop isgreater than 5 % for the radiation pulse width used. Whenmonitoring large photocurrents, care must be taken that theampe
