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Degradation of bipolar transistors at high doses obtained at elevated temperature applied during gamma-irradiation
Microelectronics Reliability xxx (xxxx) xxxx
Contents lists available at ScienceDirect
Microelectronics Reliability journal homepage: www.elsevier.com/locate/microrel
Degradation of bipolar transistors at high doses obtained at elevated temperature applied during gamma-irradiation A.S. Petrova, , K.I. Taperoa,b, A.M. Galimovc, G.I. Zebrevd ⁎
a
Research Institute of Scientific Instruments (RISI), Turaevo, 8, Lytkarino, Moscow Region 140080, Russia National University of Science and Technology MISIS, Leninsky prospect, 4, Moscow 119049, Russia c JSC MRI Progress, Cherepanovykh, 54, Moscow 125183, Russia d National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Kashirskoe shosse, 31, Moscow 115409, Russia b
ABSTRACT
The paper presents investigation results of radiation-induced change in current gain of bipolar transistors at elevated temperature applied during gamma-irradiation with high levels of dose. The regularities obtained during irradiation at elevated temperature coincide qualitatively with the data obtained previously during irradiation at low dose rate. Results of simulation confirm the possibility of applying of developed model of radiation induced degradation of bipolar transistor for irradiation at different temperatures.
1. Introduction
2. Experiment and its results
Enhanced low dose rate sensitivity (ELDRS) is one of the important features of the degradation of bipolar transistors and linear (or mixedsignal) integrated circuits. This effect is generally referred to true dose rate effects, which mean that the degradation at the end of a low dose rate irradiation is greater than the degradation measured after irradiation to the same dose at high dose rate followed by a room temperature anneal for a time at least as long as the irradiation time at low dose rate [1]. The effect was discovered in the early 1990s [2–5], however it still remains relevant. Moreover, such an effect may be inherent in other technologies, which contain bipolar structures, for example, BiCMOS technology [6–8]. In most cases the ionizing radiation tests of bipolar devices, which are susceptible to ELDRS, are typically carried out using several accelerated techniques, such as irradiation with 60Co gamma-source at the dose rate of ≤0.01 rad(Si)/s or high-dose-rate irradiation at elevated temperature (about 100 °C). TM 1019.9 defines the difference in degradation of 1.5 times and higher at low dose rate (≤0.01 rad(Si)/s) and high dose rate (50–300 rad(Si)/s) as a criterion of ELDRS. Usually, ELDRS tests are limited to a range of total ionizing doses (TID) up to 100 krad(Si), however it was shown in previous work [9] that bipolar devices can degrade more severely at high dose rate than at low dose rate after irradiation to the dose of ≥500 krad(Si) in spite of the susceptibility to ELDRS at TID < 100 krad(Si). The purpose of this work is to study the features of the degradation of bipolar transistors during high-temperature irradiation at high dose rate in the range of TID above 500 krad(Si).
The work investigates the radiation-induced change in current gain h21E of bipolar NPN (1133NT1AEP) and PNP (1133NT5AEP) transistors. These were the same devices, which were studied in the previous work [9], but these devices were taken from another lot. Studied devices were irradiated by 60Co gamma-rays at dose rate of 100 rad(Si)/s at room (25 °C) and elevated (100 °C) temperature. It was shown in [9] that the worst-case condition for the degradation of h21E of tested devices is irradiation in passive mode, so all irradiations in this study were carried out at passive mode during irradiation. Measuring of h21E was performed at Ucb = 3 V, Ie = 0.5 mA for NPN transistors and at Ucb = −3 V, Ie = 0.5 mA for PNP transistors. Figs. 1 and 2 present dependences of the change in h21E on TID for studied devices irradiated by 60Co gamma-rays at temperature of 25 °C and 100 °C respectively. Fig. 1 shows that up to TID level of 500 krad(Si) the degradation of PNP bipolar transistors is greater than that at the temperature of 100 °C. This behavior similar to that of most of bipolar devices, which are susceptible to ELDRS. However at TID levels above 500 krad(Si) dose dependence tends to saturation at the temperature of 100 °C (see Fig. 1). The similar behavior was observed previously in [9] at the case of low dose rate irradiation (see Fig. 3). Fig. 2 shows that the level of degradation of NPN bipolar transistors is more notable at the temperature of 25 °C at the whole studied range of dose. Irradiation at 100 °C leads to saturation of degradation level at the doses above 500 krad(Si).
⁎
Corresponding author. E-mail address: [email protected] (A.S. Petrov).
https://doi.org/10.1016/j.microrel.2019.06.070 Received 15 May 2019; Received in revised form 17 June 2019; Accepted 22 June 2019 0026-2714/ © 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: A.S. Petrov, et al., Microelectronics Reliability, https://doi.org/10.1016/j.microrel.2019.06.070
Microelectronics Reliability xxx (xxxx) xxxx
A.S. Petrov, et al.
Fig. 1. Increment of 1/h21E of PNP bipolar transistors during irradiation room (25 °C) and elevated (100 °C) temperature at the dose rate of 100 rad(Si)/s.
Fig. 3. Increment of 1/h21E of PNP bipolar transistors during irradiation at the dose rates of 0.015 rad(Si)/s and 50 rad(Si)/s (data from [9]).
Fig. 2. Increment of 1/h21E of NPN bipolar transistors during irradiation room (25 °C) and elevated (100 °C) temperature at the dose rate of 100 rad(Si)/s.
Fig. 4. Increment of 1/h21E of NPN bipolar transistors during irradiation at the dose rates of 0.015 rad(Si)/s and 50 rad(Si)/s (data from [9]).
3. Discussion and simulation
Dependence of degradation rate on dose rate in the range of low doses is determined by ELDRS [10]. For the same electric field in the critical areas of isolation the charge yield is less for high dose rate due to higher rate of recombination. Saturation of degradation at low dose rate is due to the balance of accumulation and thermal annealing. A weak trend to saturation at high dose rate is a consequence of the decrease of charge yield with a decrease of electric field in oxide. The built-in electric field in oxide decreases at high doses due to the accumulation of charge on defects, which field is opposite to the built-in field, caused by the contact potential difference on the electrodes. Radiation induced degradation model of the bipolar transistor was presented in [10] as the rate equations set for the variation of the dosedependent interface recombination trap density ΔNRD and the oxide charged trap density ΔNox
It was shown in previous study [9] that bipolar transistors can degrade more severely at high dose rate than at low dose rate after irradiation to the dose of ≥500–700 krad(Si) in spite of the susceptibility to ELDRS at TID < 300 krad(Si) (see Figs. 3,4,5,6 [9]). At TID levels above 500–700 krad(Si) there is the saturation of degradation at the dose rate of 0.015 rad(Si)/s. Results obtained at the temperature of 100 °C (see Figs. 1,2) are similar to results for the dose rate of 0.015 rad(Si)/s and room temperature (see Figs. 3,4). However for NPN transistors at temperature of 100 °C there is no enhanced degradation (see Figs. 2,5), and saturation level of degradation is approximately three times less than at 0.015 rad (Si)/s. This behaviour may be due to fact that devices were taken from different lots. For PNP transistors curve at temperature of 100 °C is almost identical with curve at dose rate of 0.015 rad(Si)/s. It confirms applicability of accelerated testing method using elevated temperature during irradiation for tested transistors.
d NRD (D ) = Frd K g dox dD
d Nox (D) = Fot K g dox dD 2
eff
eff
(P , Eox )
(P , Eox )
NRD (D) Pa
Nox (D) Pb
(1a) (1b)
Microelectronics Reliability xxx (xxxx) xxxx
A.S. Petrov, et al.
(when f ≪ 1) of experimental dependence. The temperature dependence of ηeff is determined by the effective energy depth of shallow hole traps in bulk oxide εp(≅0.39 eV) [11]. An observed increase in degradation for elevated temperatures and low dose rates can be explained within the framework of the single physical model, based on enhancement of the trap-assisted electronhole recombination [11]. Similar effects take place in the thick oxides of MOS devices [14]. In addition to apparent dependence of charge yield on current value of dose rate, there is also thermal annealing during irradiation determining an implicit dependence of degradation on irradiation time via Arrhenius relation for the annealing temporal constant τ. Thus, there are two different types of dose rate effects with the opposed responses to dose rate change at the fixed dose. The former (explicit dependence ηeff on irradiation temperature) increases the degradation rate with temperature at moderate doses. The latter (annealing enhancement with irradiation temperature) suppresses degradation at long term irradiation [15]. The Eqs. (1a) and (1b) are coupled by the following simple electrostatic equation for Eox.
Fig. 5. Change in 1/h21E of NPN and PNP bipolar transistors irradiated at 100 °C related to that for 25 °C versus TID, dashed line is criterion of ELDRS.
q Nox (D )
Eox (D ) = Eox 0
(4)
ox 0
The simulated inverse current gain degradation Δ1/h21E is proportional to ΔNRD and can be written as
h211 =
AS AE
r vt WB
DB
NRD
(5)
Description of the parameters used in Eqs. (1a), (1b), (4), (5), and their values obtained in [10,11] for the devices in question are summarized in Table 1. The measured and simulated dose dependences of Δ1/h21E for NPN and PNP transistors are shown in Fig. 7a and b at various temperatures of 25 and 100 °C. Table 1 Summary of modeling parameters.
Fig. 6. Change in 1/h21E of NPN and PNP bipolar transistors irradiated at 0.015 rad(Si)/s related to that for 50 rad(Si)/s versus TID (data from [9]), dashed line is criterion of ELDRS.
where ηeff(P, Eox) is the effective charge yield [11] as a function of current dose rate P and electric field in insulating oxide Eox, and D is the total dose. It is well-known that the charge yield is an increasing function of irradiation temperature T [12,13]. We argued in [10,11] that enhancement of degradatition both at low dose rates (ELDRS) and at elevated temperatures is explained by eff
(P , Eox , T ) = (Eox )
f (P , Eox , P , T )
(1 +
4f )1/2
−5
0
+
Eox / E0 (1 1 + Eox / E0
0)
Unit
Kg dox Frd
The radiation constant for SiO2 Effective oxide thickness Recombination center generation efficiency
cm−3 rad−1 μm –
Fot
Charged oxide trap generation efficiency
τa, τb
Thermal annealing temperaturedependent time Constants for recombination centers and traped charge Built-in electric field in the oxide before irradiation Electron charge Oxide dielectric permittivity Vacuum permittivity Relation of the area of the baseoxide interface to the Area of the emitter-base junction Base width Carrier's thermal velocity Carrier's capture cross-section for the energy levels located near the Si midgap The diffusivity of minority carriers in the base The energy depth of the hole shallow traps in oxides
8 × 1012 0.8 NPN 1.35 × 10−2; PNP 3.55 × 10−3 NPN 4.6 × 10−3; PNP 1.3 × 10−3; NPN 1.25 × 107; PNP 3.55 × 107 NPN 1.8 × 105; PNP 2.5 × 105 1.6 × 10−19 3.9 8.85 × 10−14 1/1
V/cm
F/cm –
0.1 107 10−15
μm cm/s cm2
10
cm2/s
0.39
eV
(2b) WB vt σr
2
where μp is hole mobility in SiO2 (~10 cm /V × s), T is irradiation temperature, kB is the Boltzmann constant. The high-field part of the charge yield dependence η(Eox) is normally interpolated by a monotonically increasing function of the internal electric field Eox
(Eox ) =
Value
q εox ε0 AS/AE
(2a)
2 q tox p (Eox ) K g P exp 2 6 ox 0 µp Eox kB T
Description
Eox0
1
2f
Parameter
DB
(3)
εp
where η0 and E0 are fitting constants, parameterizing high-field region 3
–
s
C
Microelectronics Reliability xxx (xxxx) xxxx
A.S. Petrov, et al.
irradiation [9]. For both types of transistors it is obtained the saturation of degradation for irradiation at 100 °C. It was shown that radiation induced degradation model of the bipolar transistor [10] that was developed for description of degradation at low dose rate can also be applied for explanation of high-temperature irradiation effects. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References [1] R.L. Pease, R.D. Schrimpf, D.M. Fleetwood, ELDRS in bipolar linear circuits: a review, IEEE Trans. Nucl. Sci. 56 (4) (2009) 1894–1908. [2] E.W. Enlow, R.L. Pease, W.E. Combs, et al., Response of advanced bipolar processes to ionizing radiation, IEEE Trans. Nucl. Sci. 38 (6) (1991) 1342–1351. [3] S. McClure, R.L. Pease, W. Will, G. Perry, Dependence of total dose response of bipolar linear micro-circuits on applied dose rate, IEEE Trans. Nucl. Sci. 41 (6) (1994) 2544–2549. [4] A.H. Johnston, G.M. Swift, B.G. Rax, Total dose effects in conventional bipolar transistors and linear integrated circuits, IEEE Trans. Nucl. Sci. 41 (6) (1994) 2427–2436. [5] J.T. Beaucour, T. Carriere, A. Gach, et al., Total dose effects on negative voltage regulator, IEEE Trans. Nucl. Sci. 41 (6) (1994) 2420–2426. [6] A.S. Petrov, K.I. Tapero, V.N. Ulimov, Influence of temperature and dose rate on the degradation of BiCMOS operational amplifiers during total ionizing dose testing, Microelectron. Reliab. 54 (2014) 1745–1748. [7] K.I. Tapero, A.S. Petrov, P.A. Chubunov, V.N. Ulimov, V.S. Anashin, Dose effects in CMOS operational amplifiers with bipolar and CMOS input stage at different dose rates and temperatures, 15th European Conference on Radiation and Its Effects on Components and Systems (RADECS), 2015, pp. 1–4, , https://doi.org/10.1109/ RADECS.2015.7365602. [8] A.S. Petrov, K.I. Tapero, V.N. Ulimov, A.M. Chlenov, Impact of elevated temperature applied during low dose rate irradiation on the degradation of BiCMOS operational amplifiers, Microelectron. Reliab. 88–90 (2018) 961–964. [9] A.S. Petrov, V.N. Ulimov, Some features of degradation in bipolar transistors at different test conditions for total ionizing dose effect, Microelectron. Reliab. 52 (2012) 2435–2437. [10] G.I. Zebrev, A.S. Petrov, R.G. Useinov, R.S. Ikhsanov, V.N. Ulimov, V.S. Anashin, I.V. Elushov, M.G. Drosdetsky, A.M. Galimov, Simulation of bipolar transistor degradation at various dose rates and electrical modes for high dose conditions, IEEE Trans. Nucl. Sci. 61 (4) (2014) 1785–1790. [11] G.I. Zebrev, D.Y. Pavlov, V.S. Pershenkov, A.Y. Nikiforov, A.V. Sogoyan, D.V. Boychenko, V.N. Ulimov, V.V. Emelyanov, Radiation response of bipolar transistors at irradiation temperatures and electric biases: modeling and experiment, IEEE Trans. Nucl. Sci. 53 (4) (2006) 1981–1987. [12] A.H. Johnston, R.T. Swimm, D.O. Thorbourn, Total dose effects on bipolar integrated circuits at low temperature, IEEE Trans. Nucl. Sci. 59 (6) (2012) 2995–3003. [13] A.H. Johnston, R.T. Swimm, D.O. Thorbourn, Charge yield at low electric fields: considerations for bipolar integrated circuits, IEEE Trans. Nucl. Sci. 60 (6) (2013) 4488. [14] P.A. Zimin, E.V. Mrozovskaya, P.A. Chubunov, V.S. Anashin, G.I. Zebrev, Calibration and electric characterization of p-MNOS RADFETs at different dose rates and temperatures, Accepted to publication in, Nucl. Instrum. Methods Phys. Res., Sect. A (2019), https://doi.org/10.1016/j.nima.2019.05.099. [15] G.I. Zebrev, M.G. Drosdetsky, A.M. Galimov, Non-equilibrium carrier capture, recombination and annealing in thick insulators and their impact on radiation hardness, J. Semicond. 37 (11) (2016) 111–117.
Fig. 7. Comparison between experimental (points) and simulated (lines) dose dependencies of inverse gain for of NPN (a) and PNP (b) bipolar transistors at different temperatures. Fitted parameters are as follows: (a) Frd = 1.0 × 10−2; τa (25 °C) = 1.25 × 107 s; τa (100 °C) = 1.0 × 104 s; (b) Frd = 6.0 × 10−3; τa (25 °C) = 3.55 × 107 s; τa (100 °C) = 3.55 × 104 s.
Only Frd and τa were fitted in this numerical simulation. The room temperature annealing time constant τa(25 °C) was previously assessed from the low dose rate (0.015 rad(Si)/s) experiment as ~107 s. In this work, the annealing constants at elevated temperature τa(100 °C) are found of 4 orders of magnitude lower (~104 s). Results of simulation presented at Fig. 7 confirm that suggested model adequately describe processes in bipolar transistors under irradiation at different dose rates and temperatures. 4. Conclusion Degradation of bipolar transistors at elevated temperature applied during gamma-irradiation for high dose conditions was investigated. It was shown that results of high-temperature irradiation for studied transistors are similar to those obtained previously at low dose rate
4
Contents lists available at ScienceDirect
Microelectronics Reliability journal homepage: www.elsevier.com/locate/microrel
Degradation of bipolar transistors at high doses obtained at elevated temperature applied during gamma-irradiation A.S. Petrova, , K.I. Taperoa,b, A.M. Galimovc, G.I. Zebrevd ⁎
a
Research Institute of Scientific Instruments (RISI), Turaevo, 8, Lytkarino, Moscow Region 140080, Russia National University of Science and Technology MISIS, Leninsky prospect, 4, Moscow 119049, Russia c JSC MRI Progress, Cherepanovykh, 54, Moscow 125183, Russia d National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Kashirskoe shosse, 31, Moscow 115409, Russia b
ABSTRACT
The paper presents investigation results of radiation-induced change in current gain of bipolar transistors at elevated temperature applied during gamma-irradiation with high levels of dose. The regularities obtained during irradiation at elevated temperature coincide qualitatively with the data obtained previously during irradiation at low dose rate. Results of simulation confirm the possibility of applying of developed model of radiation induced degradation of bipolar transistor for irradiation at different temperatures.
1. Introduction
2. Experiment and its results
Enhanced low dose rate sensitivity (ELDRS) is one of the important features of the degradation of bipolar transistors and linear (or mixedsignal) integrated circuits. This effect is generally referred to true dose rate effects, which mean that the degradation at the end of a low dose rate irradiation is greater than the degradation measured after irradiation to the same dose at high dose rate followed by a room temperature anneal for a time at least as long as the irradiation time at low dose rate [1]. The effect was discovered in the early 1990s [2–5], however it still remains relevant. Moreover, such an effect may be inherent in other technologies, which contain bipolar structures, for example, BiCMOS technology [6–8]. In most cases the ionizing radiation tests of bipolar devices, which are susceptible to ELDRS, are typically carried out using several accelerated techniques, such as irradiation with 60Co gamma-source at the dose rate of ≤0.01 rad(Si)/s or high-dose-rate irradiation at elevated temperature (about 100 °C). TM 1019.9 defines the difference in degradation of 1.5 times and higher at low dose rate (≤0.01 rad(Si)/s) and high dose rate (50–300 rad(Si)/s) as a criterion of ELDRS. Usually, ELDRS tests are limited to a range of total ionizing doses (TID) up to 100 krad(Si), however it was shown in previous work [9] that bipolar devices can degrade more severely at high dose rate than at low dose rate after irradiation to the dose of ≥500 krad(Si) in spite of the susceptibility to ELDRS at TID < 100 krad(Si). The purpose of this work is to study the features of the degradation of bipolar transistors during high-temperature irradiation at high dose rate in the range of TID above 500 krad(Si).
The work investigates the radiation-induced change in current gain h21E of bipolar NPN (1133NT1AEP) and PNP (1133NT5AEP) transistors. These were the same devices, which were studied in the previous work [9], but these devices were taken from another lot. Studied devices were irradiated by 60Co gamma-rays at dose rate of 100 rad(Si)/s at room (25 °C) and elevated (100 °C) temperature. It was shown in [9] that the worst-case condition for the degradation of h21E of tested devices is irradiation in passive mode, so all irradiations in this study were carried out at passive mode during irradiation. Measuring of h21E was performed at Ucb = 3 V, Ie = 0.5 mA for NPN transistors and at Ucb = −3 V, Ie = 0.5 mA for PNP transistors. Figs. 1 and 2 present dependences of the change in h21E on TID for studied devices irradiated by 60Co gamma-rays at temperature of 25 °C and 100 °C respectively. Fig. 1 shows that up to TID level of 500 krad(Si) the degradation of PNP bipolar transistors is greater than that at the temperature of 100 °C. This behavior similar to that of most of bipolar devices, which are susceptible to ELDRS. However at TID levels above 500 krad(Si) dose dependence tends to saturation at the temperature of 100 °C (see Fig. 1). The similar behavior was observed previously in [9] at the case of low dose rate irradiation (see Fig. 3). Fig. 2 shows that the level of degradation of NPN bipolar transistors is more notable at the temperature of 25 °C at the whole studied range of dose. Irradiation at 100 °C leads to saturation of degradation level at the doses above 500 krad(Si).
⁎
Corresponding author. E-mail address: [email protected] (A.S. Petrov).
https://doi.org/10.1016/j.microrel.2019.06.070 Received 15 May 2019; Received in revised form 17 June 2019; Accepted 22 June 2019 0026-2714/ © 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: A.S. Petrov, et al., Microelectronics Reliability, https://doi.org/10.1016/j.microrel.2019.06.070
Microelectronics Reliability xxx (xxxx) xxxx
A.S. Petrov, et al.
Fig. 1. Increment of 1/h21E of PNP bipolar transistors during irradiation room (25 °C) and elevated (100 °C) temperature at the dose rate of 100 rad(Si)/s.
Fig. 3. Increment of 1/h21E of PNP bipolar transistors during irradiation at the dose rates of 0.015 rad(Si)/s and 50 rad(Si)/s (data from [9]).
Fig. 2. Increment of 1/h21E of NPN bipolar transistors during irradiation room (25 °C) and elevated (100 °C) temperature at the dose rate of 100 rad(Si)/s.
Fig. 4. Increment of 1/h21E of NPN bipolar transistors during irradiation at the dose rates of 0.015 rad(Si)/s and 50 rad(Si)/s (data from [9]).
3. Discussion and simulation
Dependence of degradation rate on dose rate in the range of low doses is determined by ELDRS [10]. For the same electric field in the critical areas of isolation the charge yield is less for high dose rate due to higher rate of recombination. Saturation of degradation at low dose rate is due to the balance of accumulation and thermal annealing. A weak trend to saturation at high dose rate is a consequence of the decrease of charge yield with a decrease of electric field in oxide. The built-in electric field in oxide decreases at high doses due to the accumulation of charge on defects, which field is opposite to the built-in field, caused by the contact potential difference on the electrodes. Radiation induced degradation model of the bipolar transistor was presented in [10] as the rate equations set for the variation of the dosedependent interface recombination trap density ΔNRD and the oxide charged trap density ΔNox
It was shown in previous study [9] that bipolar transistors can degrade more severely at high dose rate than at low dose rate after irradiation to the dose of ≥500–700 krad(Si) in spite of the susceptibility to ELDRS at TID < 300 krad(Si) (see Figs. 3,4,5,6 [9]). At TID levels above 500–700 krad(Si) there is the saturation of degradation at the dose rate of 0.015 rad(Si)/s. Results obtained at the temperature of 100 °C (see Figs. 1,2) are similar to results for the dose rate of 0.015 rad(Si)/s and room temperature (see Figs. 3,4). However for NPN transistors at temperature of 100 °C there is no enhanced degradation (see Figs. 2,5), and saturation level of degradation is approximately three times less than at 0.015 rad (Si)/s. This behaviour may be due to fact that devices were taken from different lots. For PNP transistors curve at temperature of 100 °C is almost identical with curve at dose rate of 0.015 rad(Si)/s. It confirms applicability of accelerated testing method using elevated temperature during irradiation for tested transistors.
d NRD (D ) = Frd K g dox dD
d Nox (D) = Fot K g dox dD 2
eff
eff
(P , Eox )
(P , Eox )
NRD (D) Pa
Nox (D) Pb
(1a) (1b)
Microelectronics Reliability xxx (xxxx) xxxx
A.S. Petrov, et al.
(when f ≪ 1) of experimental dependence. The temperature dependence of ηeff is determined by the effective energy depth of shallow hole traps in bulk oxide εp(≅0.39 eV) [11]. An observed increase in degradation for elevated temperatures and low dose rates can be explained within the framework of the single physical model, based on enhancement of the trap-assisted electronhole recombination [11]. Similar effects take place in the thick oxides of MOS devices [14]. In addition to apparent dependence of charge yield on current value of dose rate, there is also thermal annealing during irradiation determining an implicit dependence of degradation on irradiation time via Arrhenius relation for the annealing temporal constant τ. Thus, there are two different types of dose rate effects with the opposed responses to dose rate change at the fixed dose. The former (explicit dependence ηeff on irradiation temperature) increases the degradation rate with temperature at moderate doses. The latter (annealing enhancement with irradiation temperature) suppresses degradation at long term irradiation [15]. The Eqs. (1a) and (1b) are coupled by the following simple electrostatic equation for Eox.
Fig. 5. Change in 1/h21E of NPN and PNP bipolar transistors irradiated at 100 °C related to that for 25 °C versus TID, dashed line is criterion of ELDRS.
q Nox (D )
Eox (D ) = Eox 0
(4)
ox 0
The simulated inverse current gain degradation Δ1/h21E is proportional to ΔNRD and can be written as
h211 =
AS AE
r vt WB
DB
NRD
(5)
Description of the parameters used in Eqs. (1a), (1b), (4), (5), and their values obtained in [10,11] for the devices in question are summarized in Table 1. The measured and simulated dose dependences of Δ1/h21E for NPN and PNP transistors are shown in Fig. 7a and b at various temperatures of 25 and 100 °C. Table 1 Summary of modeling parameters.
Fig. 6. Change in 1/h21E of NPN and PNP bipolar transistors irradiated at 0.015 rad(Si)/s related to that for 50 rad(Si)/s versus TID (data from [9]), dashed line is criterion of ELDRS.
where ηeff(P, Eox) is the effective charge yield [11] as a function of current dose rate P and electric field in insulating oxide Eox, and D is the total dose. It is well-known that the charge yield is an increasing function of irradiation temperature T [12,13]. We argued in [10,11] that enhancement of degradatition both at low dose rates (ELDRS) and at elevated temperatures is explained by eff
(P , Eox , T ) = (Eox )
f (P , Eox , P , T )
(1 +
4f )1/2
−5
0
+
Eox / E0 (1 1 + Eox / E0
0)
Unit
Kg dox Frd
The radiation constant for SiO2 Effective oxide thickness Recombination center generation efficiency
cm−3 rad−1 μm –
Fot
Charged oxide trap generation efficiency
τa, τb
Thermal annealing temperaturedependent time Constants for recombination centers and traped charge Built-in electric field in the oxide before irradiation Electron charge Oxide dielectric permittivity Vacuum permittivity Relation of the area of the baseoxide interface to the Area of the emitter-base junction Base width Carrier's thermal velocity Carrier's capture cross-section for the energy levels located near the Si midgap The diffusivity of minority carriers in the base The energy depth of the hole shallow traps in oxides
8 × 1012 0.8 NPN 1.35 × 10−2; PNP 3.55 × 10−3 NPN 4.6 × 10−3; PNP 1.3 × 10−3; NPN 1.25 × 107; PNP 3.55 × 107 NPN 1.8 × 105; PNP 2.5 × 105 1.6 × 10−19 3.9 8.85 × 10−14 1/1
V/cm
F/cm –
0.1 107 10−15
μm cm/s cm2
10
cm2/s
0.39
eV
(2b) WB vt σr
2
where μp is hole mobility in SiO2 (~10 cm /V × s), T is irradiation temperature, kB is the Boltzmann constant. The high-field part of the charge yield dependence η(Eox) is normally interpolated by a monotonically increasing function of the internal electric field Eox
(Eox ) =
Value
q εox ε0 AS/AE
(2a)
2 q tox p (Eox ) K g P exp 2 6 ox 0 µp Eox kB T
Description
Eox0
1
2f
Parameter
DB
(3)
εp
where η0 and E0 are fitting constants, parameterizing high-field region 3
–
s
C
Microelectronics Reliability xxx (xxxx) xxxx
A.S. Petrov, et al.
irradiation [9]. For both types of transistors it is obtained the saturation of degradation for irradiation at 100 °C. It was shown that radiation induced degradation model of the bipolar transistor [10] that was developed for description of degradation at low dose rate can also be applied for explanation of high-temperature irradiation effects. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References [1] R.L. Pease, R.D. Schrimpf, D.M. Fleetwood, ELDRS in bipolar linear circuits: a review, IEEE Trans. Nucl. Sci. 56 (4) (2009) 1894–1908. [2] E.W. Enlow, R.L. Pease, W.E. Combs, et al., Response of advanced bipolar processes to ionizing radiation, IEEE Trans. Nucl. Sci. 38 (6) (1991) 1342–1351. [3] S. McClure, R.L. Pease, W. Will, G. Perry, Dependence of total dose response of bipolar linear micro-circuits on applied dose rate, IEEE Trans. Nucl. Sci. 41 (6) (1994) 2544–2549. [4] A.H. Johnston, G.M. Swift, B.G. Rax, Total dose effects in conventional bipolar transistors and linear integrated circuits, IEEE Trans. Nucl. Sci. 41 (6) (1994) 2427–2436. [5] J.T. Beaucour, T. Carriere, A. Gach, et al., Total dose effects on negative voltage regulator, IEEE Trans. Nucl. Sci. 41 (6) (1994) 2420–2426. [6] A.S. Petrov, K.I. Tapero, V.N. Ulimov, Influence of temperature and dose rate on the degradation of BiCMOS operational amplifiers during total ionizing dose testing, Microelectron. Reliab. 54 (2014) 1745–1748. [7] K.I. Tapero, A.S. Petrov, P.A. Chubunov, V.N. Ulimov, V.S. Anashin, Dose effects in CMOS operational amplifiers with bipolar and CMOS input stage at different dose rates and temperatures, 15th European Conference on Radiation and Its Effects on Components and Systems (RADECS), 2015, pp. 1–4, , https://doi.org/10.1109/ RADECS.2015.7365602. [8] A.S. Petrov, K.I. Tapero, V.N. Ulimov, A.M. Chlenov, Impact of elevated temperature applied during low dose rate irradiation on the degradation of BiCMOS operational amplifiers, Microelectron. Reliab. 88–90 (2018) 961–964. [9] A.S. Petrov, V.N. Ulimov, Some features of degradation in bipolar transistors at different test conditions for total ionizing dose effect, Microelectron. Reliab. 52 (2012) 2435–2437. [10] G.I. Zebrev, A.S. Petrov, R.G. Useinov, R.S. Ikhsanov, V.N. Ulimov, V.S. Anashin, I.V. Elushov, M.G. Drosdetsky, A.M. Galimov, Simulation of bipolar transistor degradation at various dose rates and electrical modes for high dose conditions, IEEE Trans. Nucl. Sci. 61 (4) (2014) 1785–1790. [11] G.I. Zebrev, D.Y. Pavlov, V.S. Pershenkov, A.Y. Nikiforov, A.V. Sogoyan, D.V. Boychenko, V.N. Ulimov, V.V. Emelyanov, Radiation response of bipolar transistors at irradiation temperatures and electric biases: modeling and experiment, IEEE Trans. Nucl. Sci. 53 (4) (2006) 1981–1987. [12] A.H. Johnston, R.T. Swimm, D.O. Thorbourn, Total dose effects on bipolar integrated circuits at low temperature, IEEE Trans. Nucl. Sci. 59 (6) (2012) 2995–3003. [13] A.H. Johnston, R.T. Swimm, D.O. Thorbourn, Charge yield at low electric fields: considerations for bipolar integrated circuits, IEEE Trans. Nucl. Sci. 60 (6) (2013) 4488. [14] P.A. Zimin, E.V. Mrozovskaya, P.A. Chubunov, V.S. Anashin, G.I. Zebrev, Calibration and electric characterization of p-MNOS RADFETs at different dose rates and temperatures, Accepted to publication in, Nucl. Instrum. Methods Phys. Res., Sect. A (2019), https://doi.org/10.1016/j.nima.2019.05.099. [15] G.I. Zebrev, M.G. Drosdetsky, A.M. Galimov, Non-equilibrium carrier capture, recombination and annealing in thick insulators and their impact on radiation hardness, J. Semicond. 37 (11) (2016) 111–117.
Fig. 7. Comparison between experimental (points) and simulated (lines) dose dependencies of inverse gain for of NPN (a) and PNP (b) bipolar transistors at different temperatures. Fitted parameters are as follows: (a) Frd = 1.0 × 10−2; τa (25 °C) = 1.25 × 107 s; τa (100 °C) = 1.0 × 104 s; (b) Frd = 6.0 × 10−3; τa (25 °C) = 3.55 × 107 s; τa (100 °C) = 3.55 × 104 s.
Only Frd and τa were fitted in this numerical simulation. The room temperature annealing time constant τa(25 °C) was previously assessed from the low dose rate (0.015 rad(Si)/s) experiment as ~107 s. In this work, the annealing constants at elevated temperature τa(100 °C) are found of 4 orders of magnitude lower (~104 s). Results of simulation presented at Fig. 7 confirm that suggested model adequately describe processes in bipolar transistors under irradiation at different dose rates and temperatures. 4. Conclusion Degradation of bipolar transistors at elevated temperature applied during gamma-irradiation for high dose conditions was investigated. It was shown that results of high-temperature irradiation for studied transistors are similar to those obtained previously at low dose rate
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