J.F. Krieg

Effect of ion energy upon dielectric breakdown of the capacitor response in vertical power MOSFETs

The effect of ion energy upon the ion-induced dielectric breakdown response of the capacitor response in vertical power metal-oxide semiconductor field effect transistors (MOSFETs) was investigated. The single event gate rupture response was experimentally determined using mono-energetic ion beams of copper, niobium, and gold. Irradiations were conducted using an ion species tuned to different energies, producing a range of linear energy transfer (LET) values for that ion. Numerous MOSFETs were characterized to identify the onset of ion-induced dielectric breakdown. These data along with previously taken data demonstrated that the ion-induced dielectric breakdown cannot be adequately described in terms of LET, but is better described in terms of atomic number (Z). Based upon these observations, a new semi-empirical expression is presented describing the critical ion-induced breakdown response in terms of Z instead of LET. This expression is shown to be a better single event gate rupture model of the capacitor response.

Evaluation of proposed hardness assurance method for bipolar linear circuits with enhanced low dose rate sensitivity (ELDRS)

Data are presented on several low dose rate sensitive bipolar linear circuits to evaluate a proposed hardness assurance method. The circuits include primarily operational amplifiers and voltage comparators with a variety of sensitive components and failure modes. The proposed method, presented in 1997, includes an option between a low dose rate test at 10 mrd(Si)/s and room temperature and a 100/spl deg/C elevated temperature irradiation test at a moderate dose rate. The results of this evaluation demonstrate that a 10 mrd(Si)is test is able (in ail but one case) to bound the worst case response within a factor of 2. For the moderate dose rate, 100/spl deg/C test the worst case response is within a factor of 3 for 8 of 11 circuits, and for some circuits overpredicts the low dose rate response. The irradiation bias used for these tests often represents a more degrading bias condition than would be encountered in a typical space system application.

An updated data compendium of enhanced low dose rate sensitive (ELDRS) bipolar linear circuits

The 1996 total dose data compendium on ELDRS in bipolar linear circuits is updated. The new data include 37 data sets at high and low dose rate on 29 part types from nine manufacturers. A new table on elevated temperature irradiation has been added. References for each data set are provided.

Enhanced low dose rate sensitivity (ELDRS) of linear circuits in a space environment

To investigate the ELDRS effect in a real space environment, an experiment was designed, launched, and placed in a highly elliptical orbit in November 1997. After its deployment, the electrical responses of several bipolar transistors and linear circuits have been and continue to be recorded once during every 12-hour orbit. System dosimeters are monitored to establish an average accumulated dose per orbit. With this information, the electrical parameter data are correlated with the dosimetry data to determine the total dose response of each device. This paper updates information on the ELDRS experiment through May 14, 1999. As of this date, the experiment has been in flight for a period of 18 months and has accumulated an approximate dose of 18 krd(Si). For comparison, devices, specifically linear circuits with the same date code, were irradiated using Co-60 sources, herein defined as ground-based tests. The ground-based tests are used to evaluate two hardness assurance tests, a room temperature irradiation at 10 mrd(Si)/s and an elevated temperature irradiation at 100/spl deg/C and 10 rd(Si)/s and to evaluate the ELDRS response. To that end, irradiations were performed at room temperature, approximately 22/spl deg/C, at fixed dose rates of 100, 1, and 0.01 rd(Si)/s and at elevated temperature, approximately 100/spl deg/C, at a fixed dose rate of 10 rd(Si)/s. Currently, irradiations are being performed at room temperature at a fixed dose rate of 0.001 rd(Si)/s. Comparing the ground-based data to the flight data clearly demonstrates that enhanced parametric degradation has occurred in the flight parts. The two hardness assurance screens predicted ELDRS but the design margin for the elevated temperature test may not be adequate.

Origins of total-dose response variability in linear bipolar microcircuits

LM111 voltage comparators exhibit a wide range of total-dose-induced degradation. Simulations show this variability may be a natural consequence of the low base doping of the substrate PNP (SPNP) input transistors. Low base doping increases the SPNPs collector to base breakdown voltage, current gain, and sensitivity to small fluctuations in the radiation-induced oxide defect densities. The build-up of oxide trapped charge (N/sub OT/) and interface traps (N/sub IT/) is shown to be a function of pre-irradiation bakes. Experimental data indicate that, despite its structural similarities to the LM111, irradiated input transistors of the LM124 operational amplifier do not exhibit the same sensitivity to variations in pre-irradiation thermal cycles. Further disparities in LM111 and LM124 responses may result from a difference in the oxide defect build-up in the two part types. Variations in processing, packaging, and circuit effects are suggested as potential explanations.

First observations of enhanced low dose rate sensitivity (ELDRS) in space: One part of the MPTB experiment

Bipolar devices, most notably circuits fabricated with lateral PNP transistors (LPNP) and substrate PNP transistors (SPNP), have been observed to exhibit an enhanced low dose rate sensitivity when exposed to ionizing radiation. These dose rate sensitive bipolar devices exhibited enhanced degradation of base current in transistors and of input bias current, offset current, and/or offset voltage in linear circuits at dose rates less than 0.1 rd(Si)/s compared to devices irradiated at dose rates greater than 1 rd(Si)/s. The total dose responses of several bipolar transistors and linear circuits in a space environment are demonstrated to exhibit enhanced degradation comparable, in magnitude, to ground-based data irradiated at a dose rate of 10 mrd(Si)/s indicating that enhanced low dose rate sensitivities (ELDRS) do indeed exist in space.

Enhanced low dose rate sensitivity (ELDRS) in a voltage comparator which only utilizes complementary vertical NPN and PNP transistors

For the first time, enhanced low dose rate sensitivity (ELDRS) is reported in a vertical bipolar process. A radiation hardness assurance (RHA) test method was successfully demonstrated on a linear circuit, the HS139RH quad comparator, and its discrete transistor elements. This circuit only uses vertical NPN and PNP transistors. Radiation tests on the HS139RH were performed at 25/spl deg/C using dose rates of 50 rd(Si)/s, 100 mrd(Si)/s and 10 mrd(Si)/s, and at 100/spl deg/C using a dose rate of 10 rd(Si)/s. Tests at dose rates of 50 rd(Si)/s at 25/spl deg/C and 10 rd(Si)/s at 100/spl deg/C were performed on discrete vertical NPN and PNP transistor elements which comprise the HS139RH. Transistor and circuit responses were evaluated. The dies passivation overcoat layers were varied to examine the effect of removing a nitride layer and thinning a deposited SiO/sub 2/ (silox) layer.

Hardness assurance implications of bimodal total dose response in a bipolar linear voltage comparator

The total dose response of transistors and circuits from a single wafer lot has been measured for high and low dose rate and elevated temperature irradiations. A bimodal irradiation response is observed in the circuit response that is shown to be a result of the input transistors. Hardness assurance sampling plans are examined for their adequacy to deal with the bimodal response distributions.

Total-dose hardening of a bipolar-voltage comparator

A radiation-tolerant bipolar-voltage comparator experienced severe degradation of radiation hardness when layout of the part was redrawn and the process moved from a 4-in wafer to a 6-in wafer line. The reasons for the loss in hardness are identified, and it is shown that modifications to the design layout eliminate the problem.

ELDRS in space: an updated and expanded analysis of the bipolar ELDRS experiment on MPTB

The MPTB experiment established enhanced low dose rate sensitivity (ELDRS) in space for bipolar linear circuits. Data are updated through orbit 3719, dosimetry corrected, and displacement damage and the rate of degradation as a function of dose rate are examined with new analyses.