1、Designation: F448 11Standard Test Method forMeasuring Steady-State Primary Photocurrent1This standard is issued under the fixed designation F448; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of last revision.Anumber in
2、parentheses indicates the year of last reapproval.Asuperscriptepsilon () 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 these devices are exposed
3、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 theseprocedures for ionizing dose ra
4、tes 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, thepackage response may dominate the device response for anydevice. Additional precautions are also requi
5、red when measur-ing photocurrents of 109As/Gy(Si or Ge) or lower.1.2 Setup, calibration, and test circuit evaluation proceduresare also included in this test method.1.3 Because of the variability between device types and inthe requirements of different applications, the dose rate rangeover which any
6、 specific test is to be conducted is not given inthis test method but must be specified separately.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 This standard does not purport to address all of thesafety concerns, if a
7、ny, 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. Referenced Documents2.1 ASTM Standards:2E668 Practice for Application of Thermoluminescen
8、ce-Dosimetry (TLD) Systems for DeterminingAbsorbed Dosein Radiation-Hardness Testing of Electronic DevicesF526 Test Method for Using Calorimeters for Total DoseMeasurements in Pulsed LinearAccelerator or Flash X-rayMachines3. Terminology3.1 Definitions:3.1.1 fall time, nthe time required for a signa
9、l pulse todrop from 90 to 10 % of its steady-state value.3.1.2 photocurrent relaxation time, nthe time required forthe radiation induced photocurrent to decrease to 1/e (0.368) ofits initial value. The relaxation time depends upon therecombination-controlled photocurrent decay in the media,which is
10、often a semiconductor. The relaxation time candepend upon the temperature and the strength of theirradiation/illumination.3.1.3 primary photocurrent, nthe flow of excess chargecarriers across a p-n junction due to ionizing radiation creatingelectron-hole pairs throughout the device. The charges asso
11、ci-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 shorter).3.1.4 pulse width, nthe time a pulse-amp
12、litude remainsabove 50 % of its maximum value.3.1.5 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 beam of a linear accelerator. Both the irradia-
13、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 interference from secondary electrons are described.The
14、 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 be measured at asingle dose rate under one bias c
15、ondition if the test is designedto generate information for such a narrow application. The1This test method is under the jurisdiction of ASTM Committee F01 onElectronics and is the direct responsibility of Subcommittee F01.11 on Nuclear andSpace Radiation Effects.Current edition approved June 1, 201
16、1. Published July 2011. Originally approvedin 1975 as F448 75 T. Last previous edition approved in 2005 as F448 99(2005).DOI: 10.1520/F0448-11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards vo
17、lume 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.preferred approach, described in this test method, is to char-acterize the radiation response of a devi
18、ce in a way that isuseful to many different applications. For this purpose, theresponse to pulses at a number of different dose rates isrequired. Because of the bias dependence of the depletionvolume, it is possible that more than one bias level will berequired during the photocurrent measurements.5
19、. Significance and Use5.1 PN Junction DiodeThe steady-state photocurrent of asimple p-n junction diode is a directly measurable quantity thatcan be directly related to device response over a wide range ofionizing radiation. For more complex devices the junctionphotocurrent may not be directly relate
20、d 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, ext
21、ra 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 curren
22、t 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 photocurrentmeas
23、urement 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 th
24、e 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 Ionization
25、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 measuri
26、ng 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 beminimize
27、d 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 ci
28、rcuit. 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 metall
29、ic 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 the
30、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 semic
31、onductor 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 sharplyd
32、ue 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 10.3Sawyer, J. A., and van Lint, V. A. J., “Calculations of High-Energy Se
33、condaryElectron Emission,” Journal of Applied Physics, JAPIA, Vol 35, No 6, June 1964,pp. 17061711.FIG. 1 Ionization Radiation Pulse and Typical Primary Photocurrent ResponseF448 1126.5 Nonlinearity Nonlinearities in photocurrent responseresult from saturation effects, injection level effects on lif
34、e-times, and, in the case of bipolar transistors, a lateral biasingeffect 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 Noise Since li
35、near 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, the tempe
36、rature 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 section. Sin
37、ce 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 pulse-to-puls
38、e 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 test and
39、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 should be exer
40、cised 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 the failure
41、dose for thedevice.6.10 The test must be considered destructive if the photo-current exceeds the manufacturers absolute limit.6.11 Parasitic Circuit EffectsCircuit effects due to unin-tentional interaction with the circuit topology. Examples ofparasitic circuit effects would be capacitance, resistan
42、ce andinductance that become part of the circuit performance but arenot considered active components placed within the circuit.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 twosingl
43、e-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 consistent with g
44、oodresolution 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 be a par
45、t 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 circuit; howeve
46、r, 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 isolatio
47、n 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 ensure that
48、 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) to keep t
49、he 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 circuit,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 thisimped
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