BRITISH AEROSPACE
(DYNAMICS) LIMITED BRISTOL
RADIATION ASSESSMENT OF
ISOCOM LTD OPTOCOUPLERS
CS201, CD500, 4N55, 6N134 AND 6N140
Prepared By: A W Timmis, Radiation Effects Engineer, and D P Griffiths, Radiation Effects Engineer
Approved By: G Smith, Radiation Effects Engineer
Authorised By: A Edwards, Head of Radiation Effects Group
BT25538 ISSUE 2
BRITISH AEROSPACE (DYNAMICS) LIMITED
PO Box 5, Filton, Bristol
BS12 7QW
CONTENTS
1. INTRODUCTION
1.1. General
This report covers the radiation assessment of five optocouplers manufactured by ISOCOM Limited. The assessment was performed by the Radiation Effects Department of British Aerospace (Dynamics) Limited for ISOCOM.
1.2. Devices
The five device types assessed were
| CS201 | : Date code 8909 | (Single Opto-Coupler). |
| CD500 | : Date code 8911 | (Dual Opto-Coupler). |
| 4N55/L2 | : Date code 8835 | (Dual Opto-Coupler). |
| 6N134/L2 | : Date code 8809 | (Dual Opto-Coupler). |
| 6N140/L2 | : Date code 8829 | (Quad Opto-Coupler). |
2. OBJECTIVES
2.1. General
2.2. Neutron Fluence
2.3. Total lonising Dose
2.4. Ionising Dose Rate (Photocurrent Magnitude - Transient Upset - Burn Out)
2.1. General
The main objective of the assessment was to determine the susceptibility of the five device types to nuclear radiation. The results of these assessments may form the baseline for qualification to the radiation specifications associated with BS9000.
Electronic devices are susceptible to three distinct radiation types and the effects of each radiation type were to be assessed for each device type.
2.2. Neutron Fluence
Neutrons cause lattice damage in semiconductor devices; this damage results in a decrease in the minority carrier lifetime. This will result in a loss of output from the emitting devices, a loss of efficiency in the detector devices and a reduction of gain in bipolar amplification devices.
2.3. Total lonising Dose
lonising radiation causes bulk ionisation of all materials; this ionisation results in the creation of non radiative defects in the diffusion region of emitting devices with a resultant loss in electroluminescent efficiency. These defects will also cause a loss of efficiency in detector devices.
2.4. Ionising Dose Rate
At high rates of delivery of ionising radiation, the ionisation within regions of high electric field will result in a flow of current (photocurrent); all semiconductor devices are susceptible to this photocurrent. Significant photocurrents are produced in the majority of device technologies at dose rates greater than 1E6 Rad(Si)/second.
Photocurrent flow may effect device operation in several ways, which may be prevalent depending on the radiation environment:
2.4.1. Photocurrent Magnitude
The flow of photocurrent is a possible cause of system malfunction and the photocurrent generation rate over a range of dose rates shall be determined.
2.4.2. Transient Upset
Photocurrent flow may perturb voltage levels within a device and may manifest itself as a transient upset of output signals; this upset may persist for longer than the period of the radiation pulse due to the time dependent nature of photocurrent production. Depending on the magnitude and duration of this upset, this effect may cause system malfunction.
The dose rate at which upset occurs and the magnitude and duration at higher dose rates shall be determined.
2.4.3. Burn Out
At very high rates of delivery (= 1E10 Rad(Si)/second) the photocurrent may be sufficient to cause burn out of active regions, metallisation or bond wires. Normally active region and metallisation burn out occurs rapidly (<100µs) with bond wire burn out taking comparatively longer. Burn out results in destructive failure of a device and the survival of the device should be assessed at a suitably high dose rate.
The time taken for a device to burn out shall be determined, and the device shall be physically examined to determine the nature of the burn out.
Of the fifty samples of each device type supplied, each was numbered and the radiation assessment was split as follows:
Samples 1 to 3 : Control devices for neutron tests.
Samples 4 to 28 : Neutron tests.
Samples 29 to 38 : Linac tests.
Samples 39 to 49 : Total dose tests.
Sample 50 : Spare
3. IRRADIATION FACILITIES
3.1. Neutron Fluence
3.2. Total lonising Dose
3.3. Ionising Radiation Dose Rate
3.1. Neutron Fluence
The Pulsed neutron facility VIPER at AWE Aldermaston was used for the neutron irradiations (Reference 1). The output was energetic neutrons calibrated in terms of 1MeV equivalent damage in silicon. Throughout this report, the notation n/cm.sq. is used for neutron fluence which is taken to be neutrons per square centimetre (1MeV equivalent damage in silicon) Dosimetry was provided by AWE staff in the form of sulphur tablets. The required fluences were achieved by placing devices at set distances from the facility.
3.2. Total lonising Dose
The Cobalt-60 source at the Royal Military College of Science (Reference 2) was used for the total dose irradiations. The output was gamma rays having characteristic energies of 1.17 and 1.33MeV calibrated in terms of a radiation absorbed dose (energy deposited per unit mass) in silicon. Throughout this report, the notation Rad is used for accumulated total dose which is taken to be 100 ergs deposited per gramme of silicon. [NB: The SI unit Gray (joules per kilogramme) is equivalent to 100 Rads.] Dosimetry was provided by RMCS staff in the form of calibrated positions determined by measurements with an ionisation chamber. The required total doses were achieved by placing the devices at a set distance from the source and irradiating for the appropriate time.
3.3. Ionising Radiation Dose Rate
The linear accelerator (LINAC) at AWE Aldermaston (Reference 3) was used for dose rate irradiations. The output was energetic electrons in the range 6-10MeV calibrated in terms of radiation absorbed dose in silicon per unit time. Throughout this report the notation Rad/s is used for dose rate which is taken to be 100 ergs deposited per gramme of silicon per second. Dosimetry was provided by British Aerospace in the form of NPL calibrated PIN diodes. The required dose rates were achieved by a combination of placing the devices at set distances from the LINAC exit window and the introduction of a thin aluminium scatter plate in the beam (in the latter case the beam energy was reduced from approximately 10MeV to 6MeV). Throughout the tests, the dose rate pulse was maintained as a nominally rectangular pulse of 200ns duration.
4. TEST PROCEDURES
4.1. General
4.2. Neutron Fluence
4.3. Total Dose
4.4. Dose Rate
4.1. General
The test procedures for this assessment were based on those recommended in Reference 4. Detailed test methods employed for the assessments were based generally on standard test methods; MIL 883C methods 1017.2 (Neutron), 1019.3 (Steady State Total Dose Irradiation) and 1023 (Dose Rate Response of Linear Microcircuits): MIL STD 750C methods 1015 (Steady State Primary Photocurrent), 1017 (Neutron Irradiation) and 1019 (steady State Total Dose). Specifically the methods were consistent with British Aerospace Working Instruction VW 827-02 (Radiation Test Methods for Semiconductor Devices) which embodies the above procedures.
All tests were performed at ambient temperature. Devices 1 to 3 were allocated as control devices and were not irradiated. Device 50 was kept as a spare.
4.2. Neutron Fluence
Twenty-five devices were to be assessed for neutron degradation.
Devices 4 to 8 were irradiated at 1E11 n/cm.sq.
Devices 9 to 13 were irradiated at 3E11 n/cm.sq.
Devices 14 to 18 were irradiated at 1E12 n/cm.sq.
Devices 19 to 23 were irradiated at 3E12 n/cm.sq.
Devices 24 to 28 were irradiated at 1E13 n/cm.sq.
The primary electrical parameters were measured before irradiation and within 12 hours of irradiation. The irradiations at 1E11, 3E11 and 1E13 were performed on the first pulse (RUN 1) and those at 1E12 and 3E12 were performed on a second pulse (RUN 2). Irradiations were performed with the device pins electrically shorted with conductive foam, and the ambient temperature was 25±5°C
4.3. Total Dose
Eleven devices were to be assessed for total dose degradation. Devices 39 to 43 were irradiated in multiple steps, giving total doses of 10, 20, 30, 50, 100, 200, 300, 500 and 1000 kRad. Devices 44 and 45 were irradiated in a single 100 kRad step, 46 and 47 with a single 300 kRad step and 48 and 49 with a single 1000 kRad step. Primary electrical parameters were measured before irradiation and after each step (within 5 minutes). Devices 44 to 49 were irradiated in single steps to identify any annealing that may have occurred during the multiple step irradiations. The devices were irradiated at 100 Rad/second ± 5% with an overall accuracy of 200 Rads per step. The ambient temperature was 25±2°C. Components were connected and biased in a typical configuration during irradiation.
4.4. Dose Rate
Ten devices were to be assessed for dose rate response and degradation. Devices 29 and 30 were irradiated over a range of dose rates with device supplies at 5, 10 and 15V (if appropriate). Devices 31 to 39 were irradiated over a range of dose rates at the respective maximum supply voltage. Primary electrical parameters were measured before irradiation and after each range of dose rates at a given supply voltage. The pulse width was nominally rectangular of 200ns±10%. The ambient temperature was 25±5°C. The devices were exposed with the input diode connections shorted and the photodetector configured in a worst case representative manner.
5. TEST EQUIPMENT
5.1. General
5.2. Neutrons
5.3. Total Dose
5.4. Dose Rate
5.1. General
The five device types were characterised pre and post irradiation using a GenRad 1735 Component Test System. The electrical characteristic test conditions are given for the five device types in Tables 1 to 5 and represent as close as possible the manufacturer's test conditions, as given on the respective device data sheets. The accuracies of the test system measurements are listed in Appendix A.
The data storage and subsequent statistical analysis was performed by a Hewlett Packard 300 series computer, interfacing to the Component Test System via an RS232 interface.
Tables 6 to 10 give the results of performing the component characterisation tests with no device in the system. These tables show the compliance limits (voltages, currents, times) and indicate the variations between runs.
5.2. Neutrons
The devices were irradiated unpowered and required no additional test equipment.
5.3. Total Dose
The devices were irradiated in a powered condition with the configurations outlined in Figures 1 to 5. Five device sockets were available for each device type to allow for simultaneous multiple irradiations. The power supplies (Thurlby PL 320), and device supply currents were monitored via Fluke 75 digital multimeters.
5.4. Dose Rate
The devices were irradiated in a powered condition with the configurations outlined in Figures 6 to 10. Output responses were monitored via resistors and 50 ohm terminated cables. Photocurrents were monitored using Tektronix CT2 current transformers. The dose rate was monitored by an NPL calibrated Marconi GDI PIN diode using the standard configuration outlined in Figure 11. All transient signals were captured via Tektronix 390AD digitisers and data was sent via an IEEE 488 interface to a Hewlett Packard 300 series computer for data capture and analysis.
6. ANALYSIS
6.1. General
6.2. Neutron Fluence - (Control Devices - Irradiated Devices)
6.3. Total Dose Tests
6.4. Dose Rate Tests
6.1. General
Copious data was produced for this assessment and, as a whole, is unsuitable for inclusion in this report. Generally, the data has been reduced by calculation of the means and standard deviations.
The test results are shown in Tables 11 to 35 and are grouped for each device type. Any asterisks in place of data in the tables indicate that the test system measurement range or compliance limit was reached and the corresponding measurement was meaningless and hence not included.
The methods of data reduction applied to each set of test results are given below.
6.2. Neutron Fluence
6.2.1. Control Devices
The means and standard deviations of the three control devices were calculated for each characterisation. Provided the difference from the pre-irradiation value was less than 5%, no action was required; if the control samples changed by > 5% then a correction factor was applied to the irradiated samples, for the respective run.
6.2.2. Irradiated Devices
The pre-irradiation means and standard deviations were calculated for Devices 4 to 28. Post irradiation analysis was performed by calculating the means and standard deviations of the ratio of post/pre irradiation values for the parameter measurements of each sample.
The tables give the pre-irradiation mean and standard deviations for each parameter measured and show the degradation ratio of the mean and standard deviations of the post irradiation parameter measurements. In addition, the upper or lower 95% confidence limit (mean ± (1.65 x standard deviation); reference Appendix B) is shown as selected to reflect the worst degradation.
The tables also include a column with the heading, "limit ratio". This is the ratio by which the pre-irradiation mean measurement is within the maximum or minimum parameter limit, as defined in the Electrical Characteristics of the manufacturer's data sheets. This ratio gives an easy reference to determine where a parameter has degraded beyond the manufacturer's limits, although it must be considered that the pre-irradiation measurement and the post irradiation ratios are the mean values of a number of samples.
6.3. Total Dose Tests
No control devices were considered necessary for the total dose tests as pre and post irradiation characterisations were performed at sufficiently close times to presume that ambient environment changes would not significantly influence the measurements.
The means and standard deviations were only calculated for a group of components that were exposed simultaneously. The tables give the pre-irradiation mean and standard deviations for each of the parameters measured and show the degradation ratio by the post irradiation mean and standard deviations for each parameter. In addition, the 95% confidence limits are shown for each post irradiation parameter measurements (mean ± (1.65 x standard deviation); reference Appendix B). The upper limit is shown where an increase in parametric value represents the degradation and conversely, the lower limit is shown where a decrease represents the degradation.
The tables also include a "limit ratio" column which shows the ratio by which the pre-irradiation mean measurement is within the maximum or minimum parameter limit, as defined in the Electrical Characteristics of the manufacturer's data sheets. This ratio gives an easy reference to determine where a parameter has degraded beyond the manufacturer's limits, although it must be considered that the pre-irradiation measurements and post-irradiation ratios are the mean values of a number of samples.
6.4. Dose Rate Tests
No control devices were considered necessary for the dose rate tests as pre and post irradiation characterisations were performed at sufficiently close times to presume that ambient environment changes would not significantly influence the measurements.
Ten samples of each device were individually irradiated at a variety of increasing dose rates. The corresponding photocurrent peak values and durations were recorded.
The tables give the mean and standard deviations for each device parameter measured before irradiation. After each sequence of dose rate pulses, the degradation ratio of the mean and standard deviations of each device parameter are also shown. In addition, the upper or lower 95% confidence limit (mean ± (1.65 x standard deviation); reference Appendix B) is shown as selected to reflect the worst degradation.
The tables also include a "limit ratio" column which shows the ratio by which the pre-irradiation mean measurement is within the maximum or minimum parameter limit, as defined in the Electrical Characteristics of the manufacturer's data sheets. This ratio gives an easy reference to determine where a parameter has degraded beyond the manufacturer's limits, although it must be considered that the pre-irradiation measurements and post-irradiation ratios are the mean values of a number of samples.
7. CS201 TEST RESULTS
7.1. Neutron Fluence
7.2. Total Dose
7.3. Dose Rate
7.1. Neutron Fluence
Table 11 shows the results for the neutron control devices, characterised prior to the neutron irradiation tests and repeated prior to re-characterisation of the irradiated components after Shot 1 (RUN 1) and Shot 2 (RUN 2) VIPER exposures. These results show any measurement changes due to ambient condition changes. Any changes greater than 5% were applied to the post irradiation results to compensate for non irradiation changes.
Table 12 contains the results of the neutron fluence tests. The asterisks indicate where the GenRad Test System measurement limits were reached and the data measurements were meaningless. It can be seen that the Current Transfer Ratios degrade significantly at low fluences, being out of specification at 1E11 n/cm.sq. This is also evident by the fact that at 3E11 n/cm.sq. the VCESAT measurement has been lost, implying that the output detector transistor is not being turned on. The Ton measurements also verify this. (Note that the ratios in excess of 2 represent the compliance limit of 25.60 microseconds, as shown in Table 6.)
None of the input diode characteristics measured went out of specification. Also, none of the output detector characteristics went out of specification. All of the "coupled" characteristics showed significant degradation, the most sensitive being the current transfer ratio.
7.2. Total Dose
Tables 13a and 13b contain the results of the total dose tests.
Devices 39 to 43 were exposed up to 1M Rad in 9 increments and Devices 44 to 49 were exposed in pairs of 100k Rad, 300k Rad and 1M Rad.
The input diode characteristics all remain within specification with IR reducing to a level too low for the test system to measure accurately.
The output detector characteristics all remain within specification. The largest change was with ICEO.
The coupled characteristics experienced significant degradation, with the current transfer ratios out of specification at between 50 and 100k Rads and the Ton characteristic out of specification below 50k Rads.
Comparison of Tables 13a and 13b showed little annealing, if any, having occurred during the multiple step irradiations.
7.3. Dose Rate
The dose rate tests were performed with the input diode connections shorted together and the output transistor collector emitter voltage at +5, +10 and +15 volts with the collector current limited to 100mA in each case. Figure 6 shows the configuration for the +15V test. The photocurrent response of the output transistor varied little between +5V and +15V and so only two devices were tested at the different voltages. The other samples were all tested with +15V supply.
Table 14 contains the gamma dose rate test results performed at +15V, which shows that the CS201 survives the dose rates up to 6E9 Rad(Si)/second, with the photocurrent limited by the output transistor external collector current limiting resistor. (The effect of the current limiting is seen by the increase in photocurrent duration.) Appendix C, Figures A1 to A3, show the CS201 photocurrent response at various dose rates.
Tables 15a and 15b show the parametric degradation experienced by the device as a result of the dose rate exposures. The current transfer ratios have degraded significantly. Each sequence of dose rate tests at each supply voltage accumulate approximately 2k Rads total dose for each device. Reference to Table 13a shows that the "dose rate" degradation occurs at a lower total dose for each device. This is contrary to the typical trend in semiconductors and so must be associated with optical coupling. This potential failure mechanism must be considered and a limit to the total dose delivered during a high dose rate transient should be applied, lower than the normal total dose susceptibility of the device.
8. CD500 TEST RESULTS
8.1. Neutron Fluence
8.2. Total Dose
8.3. Dose Rate
8.1. Neutron Fluence
Table 16 shows the CD500 pre-irradiation and post RUN 1 and RUN 2 characterisation measurements. These results reflect any ambient changes and are used to adjust the post irradiation measurements for parameters that exhibit a greater than 5% shift.
Table 17 shows the neutron fluence test results. The asterisks indicate where the GenRad Test System measurement limits were reached and the data considered meaningless. No manufacturer's data was available for Ton and Toff so no limit ratio is applied to these measurements. It is apparent that the current transfer ratio is the most susceptible characteristic, exceeding the limit ratio between 1E11 and 3E11 n/cm.sq. The absence of data for VCESAT beyond 3E11 n/cm.sq. is due to the CTR degradation preventing the output transistor from being turned on with the input diode current, If, as specified in the test conditions.
The Ton parameter saturates at the test system compliance limits at 1E11 n/cm.sq. This corresponds to a turn on time of 25.6 microseconds.
The "coupled" characteristics were the only parameters that directly degraded beyond the limit ratios.
8.2. Total Dose
Tables 18a and 18b show the results of the total dose tests.
Devices 39 to 43 were exposed up to 1MRad in 9 increments and Devices 44 to 49 were exposed in pairs at 100k Rad, 300k Rad and 1M Rad.
The input diode characteristics all remain within specification, with the Ir characteristic occasionally being too low to record.
The output detector characteristics all remain within specification, with the largest change being in Iceo.
The coupled characteristics experienced significant degradation, with the current transfer ratios degradation exceeding their limit ratios between 200k Rad and 300k Rad (the sample group 44 to 49 showed slightly less CTR susceptibility; reference Table 18b). The Ton characteristic reached the measurement compliance limit as the CTR degraded but VCESAT remained within the limit ratio up to between 500k Rad and 1M Rad.
Comparison of Tables 18a and 18b showed generally little annealing having occurred during the multiple step irradiations. In fact, the CTR degradation appeared to behave contrary to multiple step annealing, but was most probably due to the statistical uncertainties associated with the small sample quantity. However, differences were only of the order of 10% and so considered reasonable.
8.3. Dose Rate
The dose rate tests were performed within input diode connections shorted together and the output transistor collector-emitter voltage at +5, +10 and +15 volts, with the collector current limited to 100mA in each case. Figure 7 shows the dose rate test circuit configured for +15V supply. The dual device was considered as two discrete devices for the purposes of the data analysis.
The photocurrent responses varied little by changing the supplies from +5V to +15V, so only two samples were tested across the voltage range whilst the other samples were tested at only +15V.
Table 19 shows the gamma dose rate test results performed at +15V. The device survived dose rates up to 6E9 Rad(Si)/second. The photocurrent levels reached the limit at 3E8 Rad/second. The effect of the current limit at higher dose rates is shown by the extended photocurrent duration. Appendix C, Figures A4 to A6, show the CD500 photocurrent response at various dose rates.
Tables 20a and 20b show the parametric degradation experienced by the device as a result of the dose rate exposures. None of the consequent permanent degradation resulting from the dose rate exceeded the limiting ratios. However, the CTR degradation is more severe for the accumulated total dose (approximately 2k Rads for each sequence of increasing dose rates) than the degradation experienced in the Cobalt 60 total dose tests (reference Table 18). A limit to the total dose accumulated should accompany any statement as to the dose rate susceptibility of the device. This limit would be lower than the actual total dose levels derived from the total dose tests.
9. 4N55 TEST RESULTS
9.1. Neutron Fluence
9.2. Total Dose
9.3. Dose Rate
9.1. Neutron Fluence
Table 21 shows the results for the neutron control devices, characterised prior to the neutron irradiation tests and then repeated prior to the re-characterisation of the irradiated components after RUN 1 and RUN 2 VIPER exposures. The results show any measurement changes due to ambient condition changes. Any changes greater than 5% were applied to the post irradiation results to compensate for non-irradiation changes.
Table 22 contains the results of the neutron fluence tests. Values shown as zero are where the parameter measurement is too small a value for the GenRad Test System configuration (eg Icch characteristics). The data shows that the 4N55 is quite tolerant to neutron fluence, with the current transfer ratios remaining within the limit ratio until between 3E12 and 1E13 n/cm.sq. At this same level, the propagation delays have increased towards their limits.
9.2. Total Dose
Tables 23a and 23b contain the results of the total dose tests.
Devices 39 to 43 were exposed in 9 increments up to IM Rad and devices 44 to 49 were exposed in pairs at 100k Rad, 300k Rad and 1M Rad.
Although some degradation was detected, the 4N55 electrical characteristics remained within the manufacturer's specification limits up to 1M Rad total dose exposure. No significant annealing was observed due to the multiple step increments.
9.3. Dose Rate
The dose rate tests were performed with the input diode connections shorted together. Three photocurrents were measured (Figure 8); CT1 monitor shorted together. Three photocurrents were measured; CT1 monitoring the photocurrent in the Channel 1 detector diode, with Vcc = Vsupply; CT2 measuring the photocurrent in the Channel 1 output transistor, with Vo = Vsupply; CT3 measuring the photocurrent in the Channel 2 output transistor, with Vo = Vsupply and Vcc = 0 volts. The output transistor collector currents were limited to approximately 16mA. The dose rate tests were performed in Samples 29 and 30 with Vsupply at +5V, +10V and +15V. All other samples were tested with Vsupply at +15V.
Table 24 contains the gamma dose rate test results performed at +15V. These show that the 4N55 survives dose rates up to 6E9 Rads(Si)/second. Photocurrents were detectable in the channel 1 transistor at lower dose rates than in the channel 2 transistor. This is due to injected base current as a result of photocurrents in the biassed detector diode. It can also be seen that photocurrent in the channel 2 transistor, without any base current sourced from its detector diode, is not detectable until 1E9 Rad/second. The photocurrent in the Channel 1 detector diode far exceeds the maximum specification limit for the output transistor base current. Although this is a transient condition, if currents of these levels are likely to be damaging, recommendation should be made to limit the detector diode source current.
Tables 25a and 25b show little parameter degradation as a result of the associated total dose accompanying the dose rate tests. Appendix C, figures A7 to A8 show photocurrent responses.
10. 6N134 TEST RESULTS
10.1. Neutron Fluence
10.2. Total Dose
10.3. Dose Rate
10.1. Neutron Fluence
Table 26 shows the results for the neutron control devices, characterised prior to the neutron irradiation tests and then repeated prior to the recharacterisation of the irradiated components after RUN 1 and RUN 2 VIPER exposures. The results show any measurement changes due to ambient condition changes The Ioh parameter is the only one that varied by more than 5% but this characteristic varies considerably from device to device and measurement to measurement so was not compensated for.
Table 27 contains the results of the neutron fluence tests. The current transfer ratio did not degrade sufficiently to be measured by the test system (greater than 320%). All the other characteristics were well within the limit ratios.
10.2. Total Dose
Tables 28a and 28b contain the results of the total dose tests.
Devices 39 to 43 were exposed in 9 increments up to 1M Rad and Devices 44 to 49 were exposed in pairs at 100k Rad, 300k Rad and 1M Rad.
Comparison of Tables 28a and 28b showed no annealing having occurred during the multiple step irradiations.
Although some slight degradation was detected, the 6N134 electrical characteristics remained well within the manufacturer's specification limits up to 1M Rad total dose exposure.
10.3. Dose Rate
The dose rate tests were performed with the device configured as shown in Figure 9. Channel 1 was biased (input diode shorted) to provide a high output and Channel 2 was biased to provide a low output (If approximately 13mA). The outputs of Channel 1 and Channel 2 (VO1 and VO2) were monitored to detect any transient upset caused by the dose rate.
Table 29 contains the results of the dose rate tests. The dose rate was monitored in the Vcc connection and had no external limit applied.
The 6N134 survived dose rates up to 6E9 Rad(Si)/second and the photocurrents caused little parametric degradation, as shown in Table 30 (all ratios are approximately one). The outputs experienced a transient upset, with the high output showing greater sensitivity. Appendix C, Figures A9 and A10 show 6N134 photocurrent responses and transient upsets for various dose rates.
11. 6N140 RESULTS
11.1. Neutron Fluence
11.2. Total Dose
11.3. Dose Rate
11.1. Neutron Fluence
Table 31 shows the results for the neutron control devices, characterised prior to the neutron irradiation tests and then repeated prior to the re-characterisation of the irradiated components after RUN 1 and RUN 2 VIPER exposures. Only selected parameters were monitored for control purposes. Due to damage to the control samples during test development, the data reduction ratios were not calculated and absolute values are given. The results show only small measurement changes due to ambient conditions, and there was no need to compensate for the ambient changes.
Table 32 contains the results of the neutron fluence tests. The current transfer ratios degraded below the limit ratio between 3E12 and 1E13 n/cm.sq. As the CTR degraded, the propagation delays were extended.
11.2 Total Dose
Tables 33a and 33b contain the results of the total dose tests.
Devices 39 to 43 were exposed in 9 increments up to 1M Rad and Devices 44 to 49 were exposed in pairs at 100k Rad, 300k Rad and 1M Rad.
The current transfer ratio, CTR1 degraded to less than the limit ratio between 30k Rad and 50k Rad, CTR2 at between 100k Rad and 200k Rad and CTR3 at greater than 1M Rad. The parameter VOL1 also degraded significantly at comparable exposures.
11.3. Dose Rate
The dose rate tests were performed with the device configured as shown in Figure 10. Channels 1 and 2 inputs were configured to set their outputs high and Channels 3 to 4 biased to set their outputs low. The outputs of Channel 1 (VOl) and Channel 3 (VO3) were monitored to detect transient upset. The photocurrent was monitored in the Vcc supply line, with no external current limiting. The supply voltage was set at +5V, +10V and +15V. (Figure 10 shows the +15V configuration.)
Table 34 contains the results of the dose rate tests. The 6N140 survived dose rates up to 6E9 Rad(Si)/second, although large photocurrents were generated. The outputs experienced transient upsets, with the normally high output being more sensitive. The electrical characteristics suffered little degradation as a result of the dose rate tests.
Appendix C, Figures A11 to A13 show photocurrent responses and transient upsets at various dose rates.
12. CONCLUSIONS
12.1. CS201 - (Neutrons - Total Dose - Dose Rate)
12.2. CD500 - (Neutrons - Total Dose - Dose Rate)
12.3. 4N55 - (Neutrons - Total Dose - Dose Rate)
12.4. 6N134 - (Neutrons - Total Dose - Dose Rate)
12.5. 6N140 - (Neutrons - Total Dose - Dose Rate)
12.1. CS201
12.1.1. Neutrons
The CS201 is very susceptible to neutrons. This device would have to be significantly degraded to be specified hard to any appreciable neutron fluence level (eg larger If and lower CTR).
12.1.2. Total Dose
Without any derating, the CS201 is hard to 50k Rad(Si).
12.1.3. Dose Rate
The CS201 is hard to 6E9 Rad(Si)/second, provided the accompanying high dose rate accumulated total dose does not exceed 2k Rad(Si). The output voltage will show transient upset (voltage drop) for the photocurrent duration (up to 14µs).
12.2. CD500
12.2.1. Neutrons
The CD500 is susceptible to neutrons, being hard only up to 1E11 n/cm.sq. This device would have to be derated to be specified as hard to any higher fluence (eg larger If and smaller CTR).
12.2.2. Total Dose
Without any derating, the CD500 is hard to 200k Rads(Si).
12.2.3. Dose Rate
The CD500 is hard to 6E9 Rad(Si)/second although any specification should apply a high dose rate accumulated dose rate not to exceed 6k Rad(Si). The output will show transient upset (voltage drop) for the photocurrent duration (up to 17µs).
12.3. 4N55
12.3.1. Neutrons
The 4N55 is hard to 3E12 n/cm.sq.
12.3.2. Total Dose
The 4N55 is hard to 1M Rad(Si).
12.3.3. Dose Rate
The 4N55 is hard to 6E9 Rad(Si)/second. The output will show transient upset (voltage drop) for the photocurrent duration (up to 5µs).
12.4. 6N134
12.4.1. Neutrons
The 6N134 is hard to 1E13 n/cm.sq.
12.4.2. Total Dose
The 6N134 is hard to 1M Rad(Si).
12.4.3. Dose Rate
The 6N134 is hard to 6E9 Rad(Si)/second. Photocurrent demands on Vcc are up to 1.5 Amps and up to 15 microseconds of transient upset to the outputs may be experienced.
12.5. 6N140
12.5.1. Neutrons
The 6N140 is hard to 3E12 n/cm.sq.
12.5.2. Total Dose
The 6N140 is hard to 30k Rad(Si). The hardness would be improved by degrading. the characteristics (eg increased If for reduced CTR).
12.5.3. Dose Rate
The 6N140 is hard to 6E9 Rad(Si)/second. Photocurrent demands on Vcc are up to 5.2 Amps. Up to 9 microseconds of transient upset to the outputs may be experienced.
[Follows in Full Report: 84 Pages of Diagrams, Tables and Graphs.]