EVALUATION OF MIL-STD-883/TEST METHOD FOR BIPOLAR LINEAR CIRCUITS

Transcription

1 EVALUATION OF MIL-STD-883/TEST METHOD 09.6 FOR BIPOLAR LINEAR CIRCUITS Introduction. Ronald Pease, RLP Research, Los Lunas, NM 8703 John Seiler, NAVSEA Crane, IN A true dose rate response was first reported in bipolar linear circuit transistors in 99 [] and in bipolar linear circuits in 994 [2-4]. In these papers it was made clear that the standard test condition in MIL-STD-883 Test Method 09 (TM09 test condition A) did not work for many bipolar linear circuits used in a low dose rate space environment. In addition, the post irradiation annealing test ( rebound test), of TM09.4 required for MOS circuits in a low dose rate environment was not conservative for bipolar linear circuits. At that time the only test that could be recommended was a low dose rate test. In 994 a model of the enhanced low dose rate sensitivity, ELDRS, was proposed that suggested an accelerated test for ELDRS consisting of irradiation at an elevated temperature [5]. Several studies have been conducted to establish the appropriate dose rate and temperature for the elevated temperature irradiation test [6-8] and recommendations were made in 997 for ELDRS tests [9]. These recommendations were incorporated in an ASTM guideline document (F892-98) Standard Guide for Ionizing Radiation (Total Dose) Effects Testing of Semiconductor Devices, which has recently been updated (F892-03). In March of 2003 TM09 was revised to include tests for bipolar linear circuits, TM09.6, consisting of a low dose rate test and an accelerated (elevated temperature irradiation) test. The purpose of this paper is to present data on four circuit types that have shown enhanced low dose rate response, to evaluate the effectiveness of the new test methods in TM09.6. TM09.6 test options. For all linear and mixed-signal circuits that are comprised of bipolar circuit elements and have not been demonstrated to be free of enhanced low dose rate sensitivity (ELDRS), there are three options for total dose testing (TM09.6 paragraph 3.3.), a) test at the agreed to dose rate, b) test at a prescribed low dose rate, or c) test at an elevated temperature. These options are shown in Fig., taken from TM09.6, Figure 2. Option a) is the standard option that allows testing at the mission dose rate or one agreed to by the procurement agency (Condition C). Option b) allows testing at 0 m for specification doses 25 krad or for a total irradiation time of 000 hours if the specification is > 25 krad (Condition D). For Condition D the test level is.5 times the specification level if the dose rate is 0 m and 2.0 times the specification level if the dose rate is > 0 m. Option c) allows testing at an irradiation temperature of 00 C with a dose rate between 0.5 and 5 to the specification dose with a parameter delta design margin of 3.0 (Condition E). For Condition E the test is limited to a specification dose of 50 krad unless it can be demonstrated that the test works above that dose. For the low dose rate tests, Condition D, the design margin or overtest factor is included because of the uncertainty in bounding the maximum enhancement that may occur at lower dose rates. The overtest factors (.5 and 2.0) are safety margins that are educated guesses, since there is not a large data base for dose rates below 0 m. For the elevated temperature tests, Condition E, no overtest factor is included since longer times at elevated temperature may cause recovery of the parts (this is also why the test is limited to 50 krad). Instead, the design margin or

2 2 safety factor is applied to the irradiation induced change in the critical parameters. The factor of 3 is based on data taken on several part types from a 998 study [0]. Determine the need for ELDRS testing See Para. 3.3 Yes No Pass Perform standard test (Para 3.6. Condition A) See Para Test at the agreed to dose rate per Para Condition C Pass Perform low dose rate test per Para Condition D. 25 krad: 0 m, dose=.5 spec 2. >25 krad: 000 hrs, dose=2 spec Pass Perform elevated temperature irradiation per Para Condition E. May be used if spec dose 50 krad (see 3.6.5) , 00 C 3. Parameter delta design margin = 3 Pass Figure. The ELDRS test flow taken from TM09.6, Figure 2. Evaluation test circuits and test conditions. For this evaluation of TM09.6 four circuit types were purchased in quantities of 00 from single date code lots; Texas Instruments LM24 quad op amp, Texas Instruments LM39 quad comparator, ON Semi (Motorola) LM224 quad op amp and ON semi LM239 quad comparator. The LM24 and LM39 are widely used in space systems and previous data on these manufacturer s parts have shown them to be ELDRS []. While widely characterized in recent years, samples from National Semiconductor were not chosen, since their current commercial process is not ELDRS, and their space qualified process is undergoing modification and has not stabilized. Five samples of each type were irradiated under bias. The irradiation bias conditions are shown in Fig. 2. The bias condition for the op amps was a voltage follower with Vcc =+5V, Vee=0V and input voltage of 0.5V for each op amp in the package. For the comparators the supply voltages were the same as for the op amps and the two inputs of each comparator were at 0.5 and V, with two outputs high and two low. The test matrix showing the dose rates, total dose levels, irradiation temperature and test facility is shown in Table.

3 3 0.5V V LM24.0V +5V + LM V K 0.5V Figure 2. Irradiation bias conditions for the LM24/LM224 (left) and LM39/LM239 (right). All electrical measurements were made at room temperature on an Eagle linear test system. While all of the basic specification parameters were measured, the only parameters to change significantly were the input bias currents (Ib+ and Ib-), the offset voltage, Vos, and the offset current, Ios. Measurements were made on all four of the circuits in each package. The test at 2.6 m is used as the baseline low dose rate test to determine if the TM09.6 tests bound the low dose rate response. The specification total dose levels were originally assumed to be 30 and 50 krad for the ON Semi parts and 50 and 00 krad for the Texas Instruments parts, for the purpose of establishing the dose rates for the 000 hour tests. These specifications lead to the dose rates of 6.7, 27.8, and 55.6 m (2X specification dose /000 hours). The high dose rate test (00 ) is used to establish the low dose rate enhancement factors as a function of dose. The elevated temperature irradiation tests were performed using a Thermostream forced air heating unit to bring the temperature of the parts up to 00 C prior to irradiation. The parts were cooled to room temperature for post irradiation electrical characterization. Table. Irradiation test matrix. Dose rate () Dose (krad) Rad Temp ( C) Test facility ,5,0,20,30,50 25 RTI 0.0 5,0,20,30,50,75,00,50 25 RTI ,45,60 (000 hrs) 25 Crane ,75,00 (000 hrs) 25 Crane ,00,200 (000 hrs) 25 Crane 0.5 0,20,30,50,00 00 Crane 5 0,20,30,50,00 00 Crane 00 0,20,30,50,00,200, Crane Test results. Data for the four most sensitive parameters, Ib+, Ib-, Vos and Ios, have been analyzed for the irradiation induced parameter change for each circuit in each package. To illustrate the raw data (not processed according to the TM09.6 design margins) Figs. 3 and 4 show the changes in Ib+ vs. dose for each of the tests listed in Table for the Texas Instruments parts and the ON Semi parts, respectively. The data are presented as the absolute values of the average changes for all circuits in each of the five packages.

4 Del Ib(0.0026) Del Ib(0.0) Del Ib(0.027) Del Ib(0.055) Del Ib(00) Del Ib(ETI-0.5) Del Ib(ETI-5) Del Ib (na) Spec Del Ib (na) 00 Spec 0 Del Ib(0.0026) Del Ib(0.0) Del Ib(0.027) Del Ib(0.055) Del Ib(00) Del Ib(ETI-0.5) Del Ib(ETI-5) Dose (krad) Dose (krad) Figure 3. Absolute value of ave. Del Ib+ vs. dose for all irradiation tests for T.I. parts with LM24 op amp on the left and LM39 comparator on the right Del Ib(0.0026) Del Ib(0.0) Del Ib(0.027) Del Ib(00) Del Ib(ETI-0.5) Del Ib(ETI-5) Del Ib (na) 00 Spec Del Ib(0.0026) Del Ib(0.0) Del Ib(0.027) Del Ib(00) Del Ib(ETI-0.5) Del Ib(ETI-5) Del Ib (na) 00 Spec Dose (krad) Dose (krad) Figure 4. Absolute value of ave. Del Ib+ vs. dose for all irradiation tests for ON Semi parts with LM224 op amp on the left and LM239 comparator on the right. From Fig. 3 we can see that the Texas Instrument parts demonstrate a very large low dose rate enhancement factor and that all low dose rate (LDR) and elevated temperature irradiation (ETI) tests result in significantly more degradation than the high dose rate (HDR) test. On the other hand the ON Semi parts, shown in Fig. 4, only demonstrate ELDRS at relatively low total dose

5 5 levels, less than 20 krad for the LM224 and less than krad for the LM239, since above these levels the HDR test results in more degradation than the 2.6 m test. Since the ON Semi parts are only ELDRS at relatively low dose levels the test method cannot be applied to these parts except at dose levels below about 20 krad. Hence the 000 hour test is not applicable to these parts. In fact the ON Semi parts proved to be a poor choice for this validation test, although previous data on these Motorola parts showed a strong ELDRS behavior. This demonstrates once again the large amount of variation that can be expected lot to lot for many ELDRS parts. The test method was applied on the T.I. parts at 25 krad and 50 krad and on the ON Semi parts at 0 krad and 20 krad. To evaluate the test method, the low dose rate test was applied at 0 m for the ON Semi parts and at 25 krad for the T.I. parts by comparing the average change in parameter at.5x the specification dose to the average change in parameter at the specification dose for the 2.6 m irradiation. For the T. I. parts at 50 k the average change in parameter at 00 krad for the 27.8 mrad was compared to the average change in parameter at 50 krad for the 2.6 m irradiation (000 hour test with design margin of 2). For the ETI tests the two extremes of the dose rate range of 0.5 to 5 were used. The average change in parameters at the specification dose were multiplied by three and compared to the average change in parameter at the specification dose at 2.6 m. The ratio of the parameter change for the LDR and ETI tests per TM09.6 to the average parameter change at 2.6 m was calculated. If this ratio exceeds one then the test is conservative and if the ratio is less than one the test is non-conservative and the TM09.6 test fails. If the degraded parameter did not exceed the pre-irradiation specification limit at the specification dose at 2.6 m, then the test was not applied, since the part would not be considered a failure in a lot acceptance test. In order to illustrate the variation that may occur for the four circuits in a quad package, the average change of the five samples was calculated for each of the four circuits within a package. Fig. 5 shows the results of the application of TM09.6 tests for the T.I. parts for an assumed specification dose of 50 krad. For this dose the LDR test is a 000 hour test at 27.8 m. The LM24 op amp is shown on the left and the LM39 comparator is shown on the right. 6 4 Ratio TM09 test to baseline Blue Del Ib+ Red Del Vos Green Del Ios Ratio TM09 test to baseline 3 2 Blue Del Ib+ Red Del Vos Green Del Ios 0 PASS 27 m 000 hour PASS ETI 5 PASS ETI to show ELDRS 0 27 m 000 hour ETI 5 ETI to show ELDRS Figure 5. Ratio of TM09.6 test to baseline 2.6 m test for T. I. parts for a spec dose of 50 krad, with the LM24 on the left and LM39 on the right.

6 6 The groups of columns show results for the 000 hour LDR test at 27.8 m, the ETI test at 5 and the ETI test at 0.5. Within each group are results for Del Ib+ (blue), Del Vos (red) and Del Ios (green). The four bars in each group are for the four circuits in a package. The notation pass indicates that the part did not fail the parameter at 2.6 m at 50 krad. The data on the right of each figure for 00 illustrates the amount of low dose rate enhancement. There are two cases where the TM09.6 ELDRS tests failed to bound the very low dose rate results. First the 000 hour test did not work for the op amps for Del Ib+. This means that the change at 00 krad and 27.8 m was not as great as the change at 50 krad at 2.6 m. The second case is the ETI test at 5 for Del Ios on the comparator. In this case there was a very large spread in results for the four circuits in the package. While the test worked for two circuits and not the other two it must be considered a failure. Fig. 6 shows the results for the ON Semi parts with the LM224 on the left for a specification dose of 0 krad and the LM239 on the right for a specification dose of 20 krad. In both cases the LDR test is at 0 m. For the op amp the offset parameters did not fail the prerad specification at 2.6 m so the test did not apply. However, for the comparator the offset parameters did exceed the pre-rad spec and the changes for the ETI test at 5, when multiplied by three, were less than the changes at 2.6 mrd/s, hence the test failed. Ratio TM09 test to baseline Blue Del Ib+ Red Del Vos Green Del Ios Ratio TM09 test to baseline Blue Del Ib+ Red Del Vos Green Del Ios pass pass pass 0 0 m ETI 5 ETI to show ELDRS 0 0 m ETI 5 ETI to show ELDRS Figure 6. Ratio of TM09.6 test to baseline 2.6 m test for ON Semi parts with LM224 on the left for a spec dose of 0 krad and the LM239 on the right for a spec dose of 20 krad. The results of the evaluation of the TM09.6 ELDRS tests are summarized for two specification levels for each of the circuit types in Tables 2 and 3. Table 2 shows the results for the T.I. parts at 25 krad and 50 krad and Table 3 shows the results for the ON Semi parts at 0 krad and 20 krad. In Table 2 the comparator is shown at the top and the op amp at the bottom. At 25 krad the LDR test is at 0 m and at 50 krad the LDR test is at 000 hours. The notation in the table is the following: yes means the test worked, i.e. the results were conservative; pass means the parameter passed the pre-rad spec at the specification dose at 2.6 m; no means the test failed for all four circuits in the package and x/4 means that only x of four circuits in the package passed the test. However, as we have stated before, if any of the circuits in the package fail, the test fails. The ETI test at 5 does not work well for offset

7 7 parameters, especially for the comparators. There was one case where the 00 hour test did not work, i.e. for Del Ib+ on the op amp at 50 krad. Table 2. Summary of TM09 validation tests for T. I. parts at 25 and 50 krad. TI comparator LM39 25 krad 50 krad Del Ib Del Ios Del Vos Del Ib Del Ios Del Vos 0 m test Yes Yes Yes 000 hr (50 krad) Yes Yes Yes ETI test at 5 Yes /4 No Yes 3/4 Yes ETI test at 0.5 Yes Yes Yes Yes Yes Yes TI op amp LM24 25 krad 50 krad Del Ib Del Ios Del Vos Del Ib Del Ios Del Vos 0 m test Yes Yes Pass 000 hr (50 krad) No Yes Pass ETI test at 5 Yes Yes Pass 3/4 Yes Pass ETI test at 0.5 Yes Yes Pass Yes Yes Pass Table 3. Summary of TM09 validation tests for ON Semi parts at 0 and 20 krad. ON Semi comparator LM239 0 krad 20 krad Del Ib Del Ios Del Vos Del Ib Del Ios Del Vos 0 m test Yes Yes Yes Yes Yes Yes ETI test at 5 Yes 3/4 3/4 Yes No 2/4 ETI test at 0.5 Yes Yes Yes Yes Yes Yes ON Semi op amp LM224 0 krad 20 krad Del Ib Del Ios Del Vos Del Ib Del Ios Del Vos 0 m test Yes Pass Pass Yes Pass Pass ETI test at 5 Yes Pass Pass Yes Pass Pass ETI test at 0.5 Yes Pass Pass Yes Pass Pass For the ON Semi parts shown in Table 3 the ETI test at 5 did not work for the comparator offset parameters. Conclusions. The latest version of MIL-STD-883/Test Method 09 for total dose, dated March 2003, includes several tests for linear and mixed-signal circuits containing bipolar elements. Four part types, previously shown to demonstrate ELDRS, were selected to evaluate the efficiency of these test options for bounding the space like low dose rate response. The parts from Texas Instruments proved to be a good choice but the parts from ON Semi only demonstrated ELDRS at low doses and were of limited usefulness for evaluating the standard. The criteria used as the baseline for the evaluation is a test at 2.6 m. The results of the evaluations are that the 0 m test and the ETI test at 0.5 worked in all cases investigated. However, the elevated temperature irradiation test at 00 C and 5 did not work for offset parameters, especially for the comparator. These results are consistent with those published in reference 8. While the

8 8 000 hour LDR test was only applied on the Texas Instruments parts, it was found not to be conservative for the op amp Ib+ parameter at 50 krads. Hence this evaluation has shown that in the next revision of TM09 the upper dose rate range for the 00 C test should probably be substantially lowered. Additional testing to evaluate the 000 hour LDR test should be done before any recommended changes to TM09 can be made. Acknowledgements This work was funded by the Defense Threat Reduction Agency Radiation Hardened Microelectronics Program. The authors would like to thank Lew Cohn, Dale Platteter, and Nathan Nowlin for technical discussions. References [] E. W. Enlow, R. L. Pease, W. E. Combs, R. D. Schrimpf and R. N. Nowlin, "Response of Advanced Bipolar Processes to Ionizing Radiation", IEEE Trans. Nuc. Sci. NS-38, No.6, , December 99. [2] S. McClure, R. L. Pease, W. Will and G. Perry, "Dependence of Total Dose Response of Bipolar Linear Microcircuits on Applied Dose Rate", IEEE Trans. Nuc. Sci. NS-4, No.6, , December 994. [3] A. H Johnston, G. M. Swift and B. G. Rax, Total Dose Effects in Conventional Bipolar Transistors and Linear Integrated Circuits, IEEE Trans. Nuc. Sci. NS-4, No.6, , December 994. [4] J. T. Beaucour, T. Carriere, A. Gach, D. Laxague and P. Poirot, Total Dose Effects on Negative Voltage Regulator, IEEE Trans. Nuc. Sci. NS-4, No.6, , December 994. [5] D. M. Fleetwood, S. L. Kosier, R. N. Nowlin, R. D. Schrimpf, R. A. Reber, Jr., M. DeLaus, P. S. Winokur, A. Wei, W. E. Combs and R. L. Pease, "Physical Mechanisms Contributing to Enhanced Bipolar Gain Degradation at Low Dose Rates", IEEE Trans. Nuc. Sci. NS-4, No.6, , December 994. [6] Witczak, S. C., R. D. Schrimpf, K. F. Galloway, D. M. Fleetwood, R. L. Pease, J. M. Puhl, D. M. Schmidt, W. E. Combs, and J. S. Suehle, "Accelerated Tests for Simulating Low Dose Rate Gain Degradation of Lateral and Substrate PNP Bipolar Junction Transistors, IEEE Trans. Nuc. Sci. NS- 43, No.6, , December 996. [7] Pease, R. L. and M. Gehlhausen, "Elevated Temperature Irradiation of Bipolar Linear Microcircuits", IEEE Trans. Nuc. Sci. NS-43, No.6, , December 996. [8] T. Carriere, R. Ecoffet and P. Poirot, Evaluation of Accelerated Total Dose Testing of Linear Bipolar Circuits, IEEE Trans. Nucl. Sci. NS-47, No.6, , December [9] Pease, R. L., L. M. Cohn, D. M. Fleetwood, M. A. Gehlhausen, T. L. Turflinger, D. B. Brown and A. H. Johnston, A Proposed Hardness Assurance Test Methodology for Bipolar Linear Circuits and Devices in a Space Ionizing Radiation Environment, IEEE Trans. Nucl. Sci. NS-44, No.6, , December 997. [0] Pease, R. L., M. Gehlhausen, J. Krieg, J. Titus, T. Turflinger, D. Emily and L. Cohn, Evaluation of Proposed Hardness Assurance Method for Bipolar Linear Circuits with Enhanced Low Dose Rate Sensitivity (ELDRS), IEEE Trans. Nucl. Sci. NS-45, No.6, December 998. [] Pease, R. L., S. McClure, A. H. Johnston, J. Gorelick, T. L. Turflinger, M. Gehlhausen, J. Krieg, T. Carriere, and M. Shaneyfelt, An Updated Compendium of Enhanced Low Dose Rate Sensitive (ELDRS) Bipolar Linear Circuits, 200 IEEE Radiation Effects Data Workshop Record, p. 27.