1、Designation: F448 11F448 18Standard 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.Anum
2、ber in parentheses indicates the year of last reapproval.Asuperscriptepsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 This test method covers the measurement of steady-stat
3、e primary photocurrent, Ipp, generated in semiconductor deviceswhen these devices are exposed to ionizing radiation. These procedures are intended for the measurement of photocurrents greaterthan 109As/Gy(Si or Ge), in cases for which the relaxation time of the device being measured is less than 25
4、% of the pulse widthof the ionizing source. The validity of these procedures for ionizing dose rates as great as 108Gy(Si or Ge)/s has been established.The procedures may be used for measurements at dose rates as great as 1010Gy(Si or Ge)/s; however, extra care must be taken.Above 108Gy/s, the packa
5、ge response may dominate the device response for any device. Additional precautions are also requiredwhen measuring photocurrents of 109 As/Gy(Si or Ge) or lower.1.2 Setup, calibration, and test circuit evaluation procedures are also included in this test method.1.3 Because of the variability betwee
6、n device types and in the requirements of different applications, the dose rate range overwhich any specific test is to be conducted is not given in this test method but must be specified separately.1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are i
7、ncluded in this standard.1.5 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 safety, health, and healthenvironmental practices and determine theapplicability of
8、 regulatory limitations prior to use.1.6 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade
9、Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2E668 Practice for Application of Thermoluminescence-Dosimetry (TLD) Systems for Determining Absorbed Dose inRadiation-Hardness Testing of Electronic DevicesF526 Test Method for Using Calorimeters for
10、Total Dose Measurements in Pulsed Linear Accelerator or Flash X-ray Machines3. Terminology3.1 Definitions:3.1.1 fall time, nthe time required for a signal pulse to drop from 90 to 10 % of its steady-state value.3.1.2 photocurrent relaxation time, nthe time required for the radiation induced photocur
11、rent to decrease to 1/e (0.368) of itsinitial value. The relaxation time depends upon the recombination-controlled photocurrent decay in the media, which is often asemiconductor. The relaxation time can depend upon the temperature and the strength of the irradiation/illumination.3.1.3 primary photoc
12、urrent, nthe flow of excess charge carriers across a p-n junction due to ionizing radiation creatingelectron-hole pairs throughout the device. The charges associated with this current are only those produced in the junctiondepletion region and in the bulk semiconductor material approximately one dif
13、fusion length on either side of the depletion region(or to the end of the semiconductor material, whichever is shorter).1 This test method is under the jurisdiction of ASTM Committee F01 on Electronics and is the direct responsibility of Subcommittee F01.11 on Nuclear and SpaceRadiation Effects.Curr
14、ent edition approved June 1, 2011March 1, 2018. Published July 2011April 2018. Originally approved in 1975 as F448 75 T. Last previous edition approved in20052011 as F448 99F448 11.(2005). DOI: 10.1520/F0448-11.10.1520/F0448-18.2 For referencedASTM standards, visit theASTM website, www.astm.org, or
15、contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have
16、 been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official docu
17、ment.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.4 pulse width, nthe time a pulse-amplitude remains above 50 % of its maximum value.3.1.5 rise time, nthe time required for a signal pulse to rise from 10 to 90 % of its steady-s
18、tate value.4. Summary of Test Method4.1 In this test method, the test device is irradiated in the primary electron beam of a linear accelerator. Both the irradiation pulseand junction current (Fig. 1) are displayed and recorded. Placement of a thin, low atomic number (Z13) scattering plate in thebea
19、m is recommended to improve beam uniformity; the consequences of the use of a scattering plate relating to interference fromsecondary electrons are described. The total dose is measured by an auxiliary dosimeter. The steady-state values of the dose rateand junction current and the relaxation time of
20、 the junction current are determined from the data trace and total dose.4.2 In special cases, these parameters may be measured at a single dose rate under one bias condition if the test is designed togenerate information for such a narrow application. The preferred approach, described in this test m
21、ethod, is to characterize theradiation response of a device in a way that is useful to many different applications. For this purpose, the response to pulses at anumber of different dose rates is required. Because of the bias dependence of the depletion volume, it is possible that more thanone bias l
22、evel will be required during the photocurrent measurements.5. Significance and Use5.1 PN Junction DiodeThe steady-state photocurrent of a simple p-n junction diode is a directly measurable quantity that canbe directly related to device response over a wide range of ionizing radiation. For more compl
23、ex devices the junction photocurrentmay not be directly related to device response.5.2 Zener Diode In this device, the effect of the photocurrent on the Zener voltage rather than the photocurrent itself is usuallymost important. The device is most appropriately tested while biased in the Zener regio
24、n. In testing Zener diodes or precisionvoltage regulators, extra precaution must be taken to make certain the photocurrent generated in the device during irradiations doesnot cause the voltage across the device to change during the test.5.3 Bipolar TransistorAs device geometries dictate that photocu
25、rrent from the base-collector junction be much greater thancurrent from the base-emitter junction, measurements are usually made only on the collector-base junction with emitter open;however, sometimes, to obtain data for computer-aided circuit analysis, the emitter-base junction photocurrent is als
26、o measured.5.4 Junction Field-Effect DeviceA proper photocurrent measurement requires that the source be shorted (dc) to the drainduring measurement of the gate-channel photocurrent. In tetrode-connected devices, the two gate-channel junctions should bemonitored separately.5.5 Insulated Gate Field-E
27、ffect DeviceIn this type of device, the true photocurrent is between the substrate and the channel,source, and drain regions. A current which can generate voltage that will turn on the device may be measured by the techniqueused here, but it is due to induced conductivity in the gate insulator and t
28、hus is not a junction photocurrent.6. Interferences6.1 Air Ionization A spurious component of the current measured during a photocurrent test can result from conductionthrough air ionized by the irradiation pulse. Although this is not likely to be a serious problem for photocurrents greater than 109
29、As/Gy(Si or Ge), the spurious contribution can easily be checked by measuring the current while irradiating the test fixture in theabsence of a test device. Air ionization contributions to the observed signal are proportional to applied field, while those due tosecondary emission effects (see 6.2) a
30、re not. The effects of air ionization external to the device may be minimized by coatingexposed leads with a thick layer of paraffin, silicone rubber, or nonconductive enamel or by making the measurement in vacuum.FIG. 1 Ionization Radiation Pulse and Typical Primary Photocurrent ResponseF448 1826.2
31、 Secondary Emission3Another spurious component of the measured current can result from charge emission from, orcharge injection into, the test device and test circuit. This may be minimized by shielding the surrounding circuitry and irradiatingonly the minimum area necessary to ensure irradiation of
32、 the test device. Reasonable estimates of the magnitude to be expectedof current resulting from secondary-emission effects can be made based on the area of metallic target materials irradiated. Valuesgenerally range between 10 11 and 10 9 As/cm2Gy, but the use of a scatter plate with an intense beam
33、 may increase this current.6.3 Orientation The effective dose to a semiconductor junction can be altered by changing the orientation of the test unit withrespect to the irradiating electron beam. Most transistors and diodes may be considered “thin samples (in terms of the range ofthe irradiating ele
34、ctrons). However, high-power devices may have mounting studs or thick-walled cases that can act to scatter theincident beam, thereby reducing the dose received by the semiconductor chip. Care must be taken in the mounting of such devices.6.4 BiasAs the effective volume for the generation of photocur
35、rent in p-n junction devices includes the space-charge region,Ipp may be dependent on applied voltage. As applied voltages approach the breakdown voltage, Ipp increases sharply due toavalanche multiplication. If the application of the test device is known, actual bias values should be used in the te
36、st. If theapplication is not known, follow the methods for checking the bias dependence given in Section 10.6.5 Nonlinearity Nonlinearities in photocurrent response result from saturation effects, injection level effects on lifetimes,and, in the case of bipolar transistors, a lateral biasing effect
37、which introduces a component of secondary photocurrent into theprimary photocurrent measurement.4 For these reasons, photocurrent measurements must generally be made over a wide range ofdose rates.6.6 Electrical Noise Since linear accelerator facilities are inherent sources of r-f electrical noise,
38、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 on junction temperature; hence, the temperature of the test should becontrolled. Unless otherwise agreed upon by
39、 the parties to the test, measurements will be made at room temperature (23 6 5C).6.8 Beam Homogeneity and Pulse-to-Pulse RepeatabilityThe intensity of a beam from a linear accelerator is likely to varyacross its cross section. Since the pulse-shape monitor is placed at a different location from the
40、 device under test, the measureddose rate may be different from the dose rate to which the device was exposed. The spatial distribution and intensity of the beammay also vary from pulse to pulse. The beam homogeneity and pulse-to-pulse repeatability associated with a particular linearaccelerator sho
41、uld be established by a thorough characterization of its electron beam prior to performing a photocurrentmeasurement.6.9 Ionizing Dose Each pulse of the linear accelerator imparts a dose of radiation to both the device under test and the deviceused for dosimetry. The ionizing dose deposited in a sem
42、iconductor device can change its operating characteristics. As a result,the photocurrent that is measured after several pulses may be different from the photocurrent that is characteristic of an unirradiateddevice. Care should be exercised to ensure that the ionizing dose delivered to the device und
43、er test is as low as possible consistentwith the requirements for a given dose rate and steady-state conditions. Generally, this is done by minimizing the number of pulsesthe device receives. The dose must not exceed 10 % of the failure dose for the device.6.10 The test must be considered destructiv
44、e if the photocurrent exceeds the manufacturers absolute limit.6.11 Parasitic Circuit EffectsCircuit effects due to unintentional interaction with the circuit topology. Examples of parasiticcircuit effects would be capacitance, resistance and inductance that become part of the circuit performance bu
45、t are not consideredactive components placed within the circuit.7. Apparatus7.1 Regulated dc Power Supply, with floating output to produce the voltages required to bias the junction.7.2 Oscilloscopes Either a single dual-beam, or two single-beam oscilloscopes that have adequate bandwidth capability
46、ofboth main frames and plug-ins to ensure that radiation response and peak steady-state values are accurately displayed.7.2.1 Oscilloscope Camera(s) and Film, capable of recording single transient traces at a sweep rate consistent with goodresolution at the pulse widths used in the test.7.2 Digitize
47、rs with Bandwidth, Sampling Interval, and Time-base Capabilities, Oscilloscopesadequate for handling thetransient signals with good resolution for all pulse widths utilized in the test may be used. Hard copy printouts of the recordedsignal may be a part of the capability of this apparatus.digitizing
48、 oscilloscopes capable of recording single transient traces that haveadequate bandwidth capability to ensure that radiation response and peak steady-state values are accurately displayed.3 Sawyer, J. A., and van Lint, V. A. J., “Calculations of High-Energy Secondary Electron Emission,” Journal of Ap
49、plied Physics, JAPIA, Vol 35, No 6, June 1964, pp.17061711.4 Habing, D. H., and Wirth, J. L., “Anomalous Photocurrent Generation in Transistor Structures,” IEEE Transactions on Nuclear Science, IETNA, Vol NS-13, No 6,December 1966, pp. 8694.F448 1837.2.1 Digitizers with Bandwidth, Sampling Interval, and Time-base Capabilities, adequate for handling the transient signals withgood resolution for all pulse widths utilized in the test may be used. Hard copy printouts of the recorded signal may be a part ofthe capability of this apparatus.7.
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