Pergamon Microelectron. Reliab., Vol. 37, No. 9, pp. 1367-1373, 1997

© 1995 IEEE. Published by Elsevier Science Ltd Printed in Great Britain

PII: S0026-2714(97)00008-5 0026-2714/97 $17.00 + 0.00

MOSFET PREDICTION IN SPACE ENVIRONMENTSt

I. N. SHVETZOV-SHILOVSKY Moscow Physics and Engineering Institute, Kashird Koe Sh 31, 115409 Moscow, Russia

Abstract--This paper gives the approach to the predictionof MOSFET response in space environments based on mathematical modeling. The appropriate model, called the Conversion model, is developed for the description of the numbers of oxide trapped charges and interface states as functions of irradiation dose and annealing time. The central point of this model is the numerical relationship between oxide charge annealing and interface states build-up. The dependence of the annealing process on time can be described by linear response theory, as well as on the basis of a more generalized approach, taking into account tunneling and thermal effects. Parameters of the model are extracted from characteristics, obtained in laboratory tests, when transistors are irradiated at relatively high dose rates with X-rays and then annealed. The results can be extrapolated to the range of dose rates, typical for space applications. For implementation of conversion model predictions in circuit simulation they are converted into the shifts of MOSFET parameters for SPICE. © 1995 IEEE. Published by Elsevier Science Ltd.

1. INTRODUCTION

Since low dose-rate testing at dose rates, typical of natural space, is relatively time consuming and expensive, the MOSFETs response prediction in space environments has been of interest for many years [1-5]. The techniques of prediction can be divided into two groups, giving two principal approaches to the solution of this problem. The first approach is based on the simulation of space radiation effects on the MOS structure with the help of high dose-rate irradiation followed by specially adjusted annealing. The most popular technique following this approach is the MIL-STD-883D method 1019.4 [6] . This procedure, including irradiation at 50-300rad(Si)/s and 168h thermal annealing at 100°C, provides an estimate of worst- case response at low dose-rate for the devices exhibiting a significant rebound effect [5]. The versions of the technique where the quick radiation stimulated annealing is used instead of the thermal one, are also suggested [7]. Method 1019.4 is found to be extremely useful in providing bounds for the threshold voltage shift, AV~h. However, it is not able to provide an exact estimation of A V,h due to low dose-rate irradiation [8]. In spite of several attempts which have been undertaken to make it more universal [3-5, 8], this technique is primarily intended as a pass/fail test, and its results can hardly be implemented at the stage of technological and circuit design.

The second approqach to the MOSFETs predic- tion in space environments [9] is more suitable for the

t© 1995 IEEE. Reprinted, with permission, from Proceedings of 20th International Conference on Micro- electronics, NiL 12-14 September 1995, Vol. 1, pp. 183-188.

1367

design and is aimed at radiation hardness assurance. It is based on the implementation of mathematical models of irradiation and annealing processes. Models must be developed for two major basic effects, contributing to the change of MOSFETs characteristics. These are the growth of oxide trapped charge with density ANo~ and the generation of interface traps with density AN,. It is important for the models to be valid in the wide range of dose rates and annealing periods. This is possible due to a very important experimental fact [10, 11]: the fundamental rates of defects growth and annealing processes are independent from dose rate. Extracting these par- ameters from experimental data received in labora- tory tests, one can use the extrapolation technique to obtain MOSFETs characteristics in space environ- ments.

Several problems preventing the application of the second approach have to be solved:

(i) While the processes of hole trapping and annealing of oxide space charge are relatively well understood [1, 12-14], a suitable model for interface traps build-up is still absent.

(ii) The description of time dependent effects in oxide trapped charge annealing, based on the tunneling front concept and application of linear theory [12-14], needs to include cases when tunneling is not the only mechanism of charge loss in oxide. The modified model must be able to describe the specific effects for very low dose-rate irradiation [15, 16].

(iii) The practical implementation of predictions results in circuit design calls for the establish- ment of equations which can be used to calculate the parameters of transistors models for circuit simulation.

1368 I. N. Shvetzov-Shiiovsky

The purpose of this paper is to give the approach to the solution of the above mentioned problems. The convenient model for interface build-up is developed and experimentally verified. The general- ized description of oxide trapped charge anneal, accounting for thermal and radiation stimulated annealing, is proposed. Finally, the parameters extraction procedure for models used in circuit simulation is developed, and the variation of parameters under irradiation and annealing are investigated.

2. EXPERIMENTAL DETAILS

All irradiations were carried out on the 40 kV Cu-anode X-ray source with dose rates up to 2000 rad(SiO2)/s. The dosimetry control was per- formed with an ionizing chamber detector and a silicon p-i-n diode. The samples were n- and p-channel MOSFETs with 100 nm (A1) and 30 nm (polysilicon) gate oxide thickness. The transistors were irradiated in open air with different biases on the gate and all other terminals were grounded. Irradiation and annealing were performed at a temperature of 30 + 0.1°C. Electrical measurements were done in the linear region of device operation with a drain voltage of 100 mV and constant range of drain currents. To eliminate the influence of bias changing during measurements, the electrical tests took less than 1% of total time. To avoid the influence of transistor parameters on the results of experiments during the investigations of the anneal- ing process under different oxide fields, the samples were reused after 400°C annealing.

3. CONVERSION MODEL

The total radiation induced threshold voltage shift A V~h can be separated into two components due to oxide trapped charge (A VoO and interface traps (A V~,) charge build-up:

AV,, = AVo, + A~,. (l)

Usually the analytical descriptions of dependencies on time for the two components are given by different formal equations for A V~, and A Vo,. This increases the number of fitting constants to be extracted when the prediction technique is used and limits the possibili- ties in the prediction of the influence of external conditions (temperature, electric field, etc.).

The conversion model for interface traps charge build-up is based on the fact revealed by Lai [17] that during the annealing of oxide trapped charge, introduced by irradiation, the number of interface traps built correlates with the decrease of positive charge. Persbenkov et al. [18] gave the numerical model for this relationship, introducing conversion coefficient Ko~, which reflects the strong linear correlation between the build-up of interface traps and hole annealing.

The existence of linear correlation has been checked using reported experiments [10, 19-21], as well as our experimental results. To obtain ANo, and AN~,, experimental data on A V,, and mobility have been analyzed using the Galloway charge separation technique [22]• Typical separation results for a 100 nm gate oxide nMOSFET are shown in Fig. 1. The values of linear correlation coefficients for different experiments are in the range of 0.85--0.95. The numerous data obtained give the possibility of

1 . 2 2

(a)

p ,

(b)

ANit, x l O H c m - 2 2.8

1 . 2 0

1.18

/ !.16 ...:::?.

1 . 1 4 i i wnw i wlw I i w w ww v i l l i IIW ' W l l ' ' W IV" I ' ' ' ' ' ' I

-0.2 0.0 0.2 0.4 0.6

A V t h , V

2 . 6

2 . 4

2 . 2

2 . 0

B '~ ' " r

• - . ' i l k .

" " s . .

•" . '~.i ." - ::..--. :

, , , , I , , , , i , . , , . , H , i , , , , , , . 1 , 1 . . , . . , , , , i . , , . , , . . l l

1.4 ! .6 1.8 2.0 2.2 2.4

A N o t , x IO 1 lcm -2

Fig. 1, The correlation between mobility degradation and threshold voltage shift (a) and between interface states build-up and oxide trapped charges annealing (b) for a 100 nm oxide nMOSFET after 2 krad (SiO2)

I00 s pulse X-ray irradiation•

MOSFET prediction

testing the general linear hypothesis in a regression situation, estimating the mean square for pure error using approximately repeated samples [23]. For all experiments the hypothesis of linear dependence of AN~, on ANo, is not controversial with a confidence level of 95%.

The linear dependence between the two processes makes possible the development of a model, where equations for time dependent parts of both components of A V, h have the same set of internal parameters. Suppose the transistor is irradiated up to the dose D. If no annealing occurs, the amount of oxide trapped charges would reach their maximum value equal to ANoD, where ANo is a constant, giving the number of charges introduced by irradiation with unit dose. The loss of oxide trapped charges due to the annealing process, ANoa is given by:

ANo~ = DANo(1 - F(t)), (2)

where time dependent term F(t) gives the changes with time t in the number of charges residing in oxide, with F ( 0 ) = 1 and F (oo)= 0. Taking into account the assumption about charge conversion with efficiency Ko, and the fact that ANiD (AN, = constant) interface traps are introduced directly by the effect of irradiation, one can have for the amount of charges:

AN~, = (AN~ + Ko~ANo)D - Ko~ANoDF(t) (3)

ANo, = DANoF(t).

The radiation hardened thin oxide nMOSFETs used in the experiments exhibit the residual stable part of oxide trapped charge which is not annealed under normal conditions and is low field in oxide [24]. In this case, eqn (3) can be modified by introducing the additional constant ANos, giving the stable part of oxide trapped charges:

AN~t = [AN~ + Ko~(ANo - ANo,)]D

- Koi(ANo - ANos)DF(t)

ANo, = DANoF(t) + ANosD[1 - F(t)]. (4)

The appropriate equations for threshold voltage shift components are:

a V~, = + [A V~ + Ko,(a Vo - a Vos)]

- Ko,(A Vo -- AVo~)DF(t)

AI/o, = -- [DAVoF(t) + AVoiD[1 - F(t)]], (5)

where A ~ , AVo and AI/~ are constants, + is used for nMOSFET and - for pMOSFET. The extraction of the parameters of eqn (5) for different fields in oxide during annealing gives the dependence of Ko~ and AVo, on gate potential, Fig. 2. For a 100 nm gate oxide radiation soft nMOSFET, A Vo, at any field is equal to zero.

in space environments

Koi, AVos/AVo

0.5

0.4

1369

0.3 tn 1

0.2

0.1

~ - ~ , - - . - , ~ II 0.0 . . . . . . . ° ' | . . . . . . . . . i , , , , , , , , , I . . . . . . . . . i . . . . . . . . . t . . . . . . . . ~ . . . . . . . . i

0 1 2 3 4 5 6 7

Vg, V

Fig. 2. The dependence of conversion model parameters, extracted for an 30 nm oxide nMOSFET on gate potential during annealing after 2 krad (SiO2)/s 500 s irradiation

(1--Ko,; 2--AVoJAVo).

4. ANALYSIS OF TIME DEPENDENT TERM IN CONVERSION MODEL

The linear response analysis is usually applied to the modeling of radiation induced trapped holes anneal in oxide. In this case the time dependent term F(t), used in eqns (2)-(5) is given by the convolution integral [12-14]. If the beginning of the time scale coincides with the start of irradiation that is characterized by the dose-rate function 7(0, it can be written as:

F(t) = 7(t')f(t - t')dt', (6)

where f ( t ) is the impulse response function (the reaction of the system to an infinitesimally short irradiation pulse of unit dose). It is shown [25] that in the case of uniform distribution of oxide trapped charges and tunneling mechanism of charge loss:

f ( t ) = 1 - v In(t), (7)

where v is a fitting constant. To provide the validity of eqn (6) for t > exp(1/v) and t ~ 0, a more com- plicated form is used for f(t):

f ( t ) = (1 + t/to)-", (8)

where to is a fitting constant. Equation (6) provides an exact description of

the results of laboratory tests when irradiation is followed by annealing at room temperature, but fails in cases of temperature or radiation stimulated annealing. Difficulties can also be encountered if eqn (6) is implemented to the extremely low dose-rate irradiations [15,16]. The reason resides in the limitations of linear response theory aimed at the description of transient processes, while the charge inducing and annealing in space environments are close to steady-state conditions when No, is constant and Nit grows linearly with time. The time when such

1370 I. N. Shvetzov-Shilovsky

conditions are established must be close to the period of annealing of the greater part of oxide trapped charge, introduced by a short irradiation pulse. Consider the typical values of v in eqns (7) and (8), it will happen after 108-109 s at 25°C. If the annealing is stimulated by temperature or some kind of irradiation, the discrepancies between the linear response prediction and experiments can be noticed in the typical laboratory tests range of time.

Our goal is to introduce a new form for the time dependent term of conversion model F(t) without linear response theory limitations. Suppose that the annealing processes for different traps in oxide are independent. It is evident that values of annealing time z for trapped holes are different. The annealing time distribution can be explained by different position of traps in oxide that influence the rate of tunneling. The distribution of trap depths that provides different rates of annealing through thermal emission, must also be taken into account. Consider the group of traps whose discharging times are in the range (~,z + 6z). In linear response theory the traps are also grouped, but the principle of grouping resides on the moment of trap charging. It results in the physically absurd necessity of accounting for the process of traps "growing old".

The fission law can be applied to the description of discharge for separate group of traps with constant r. Assume that (i) the probability of having a charged trap with r is proportional to the amount of uncharged traps with this value of annealing time in oxide; (ii) the percentage of charged traps is small. Then, the number n of charges traps with z~(z,~ + 6z) can be found from the equation:

dn n - - - + 7ANoP(T)~ST, (9)

dt z

where P(z) is a function describing the annealing time distribution of traps. Integrating the well-known solution of eqn (9) into the range of annealing times, gives for a constant irradiation field:

ANot(y,t) = yANo(z)

× (i - I ~°''re(~)exN: t/~)d~, (lO) J,°,o <~> /

where z~o and Z~a~ are the minimal and maximal values of annealing time for the traps in oxide; ( z ) is the medium value of annealing time:

f Xmax

( z ) = ~P(Qd~. (11) ~ T m i n

Note that, although in eqns (9) and (10), 7 and P(~) are supposedly time independent and ANo is taken to be independent of z, it is easy to introduce the appropriate dependencies, unlike the linear response theory formalism, where it can be done only for a limited amount of particular cases.

Equations (9) and (10) can also be applied to the

description of transient processes. The general form of a response funtion can be found, if it assumed that 7 :~ 0 at t = 0, providing D = 1 and y = 0 for t > 0:

f ( t ) = P(z)exp( - t / z )dr . (12) rain

At a certain moment of time t the integral in eqn (12) can be separated into two parts with limits, respectively, from Zm~n to t and from t to z . . . . For z < t the exponential term in eqn (12) is small and if its decrease is not compensated for by the growth of P(z) at r--,0, the first integral is close to zero. Assume that the annealing time distribution is due to the position with respect to the Si-SiO2 interface, i.e. the charge is annealed through a tunneling process. Then, eqn (12) describes the moving of a front: at any time the charges behind the front are annealed while before it the traps do not lose their charges [the exponential term in eqn (12) at t < z is close to l].

Suppose that the distribution of traps is uniform in some region of oxide with borders Xm~, and Xm~x with zero trap density outside this region. If electron tunneling from Si dominates in the annealing process and the discharge time grows exponentially with the distance from the Si-SiO2 interface, it can be written for P(z):

P ( Q = [zln(zm,x/Zmin)] I, (13)

where Zmax and rm~n are annealing times at distances Xm~x and x~n from the interface. Substitution of eqn (13) into (12) with a lower limit equal to t, gives for the response function:

f ( t ) = ln(~m,x) + Y-{[ ( -1) ' - (-t/zm,~)']/(i!i)} - In(t) ln(r~/'t'mi~)

(14)

For z~<<t<<zm,~ the sum of the series can be found numerically and f ( t ) , given by eqn (14), decreases with time at the same rate as f ( t ) in eqn (7) with v ~ [ln(zm~) - 0.797] -I,

Consider the experiments when MOSFETs are irradiated up to the same dose with different dose rates (D = t7 = const) [15, 16]. For 7 ~ 0 eqn (10) gives, in this case, A Vo~ ~ 7, while the linear response theory predicts AVo~ ~ 7'. With typical values of v << 1, the difference between two predictions is very large. The experimental fact: d(AVo~/dy--*0 at y--*0 obtained in Refs [! 5, 16], shows that eqn (10) is closer to experiment.

5. USE OF CONVERSION MODEL IN CIRCUIT SIMULATION

For implementation of conversion model predic- tions in circuit design, they must be converted into the shifts of parameters for some circuit simulation program, e.g. SPICE. The MOSFET parameters used in this program can be calculated with the help of physical modeling if the values of ANo, and AN~,

MOSFET prediction

are given. The other way is based on the suggestion that all time dependent processes in MOSFET under irradiation and annealing can be described by the same time dependent term F ( t ) . It gives the possibility of extracting the model parameters from experimen- tal data in laboratory tests and then implementing the conversion model directly to the parameters, and predicting their values in space environments. This way seems to be more suitable for practical use of the method.

To implement this approach, a special procedure for parameters extraction has been developed, because the straightforward minimization of differ- ences between measured data and values predicted by the model, usually gives a physcially absurd solution by a numerical method. This is caused by local minimums of the error function (e.g. residual least squares) between measurements and model. To get the meaningful solution the extraction procedure must be as linear as possible, because the linear least square method gives only one solution; the model must be checked in order to eliminate correlated parameters and the optimization method must be oriented to the searching of a global minimum. The appropriate form of the SPICE level three model can be found by implementation of experimental data in model equations for linear and saturation regions of MOSFET characteristics:

IDS = Beta "/i + (Beta. ETA) . ~ + THETA .f~,

~ (Vg~ - VTO). Vd~ - 0.5- ~s .(1 + Fb), = (linear region)

ft ] 0 . 5 '(Vgs - VTO)2(I + Fb),

L (saturation region);

r V~s, (linear region)

f~ = .~ (Vg, - VTO). Vd, l ( l + Fb),

L (saturation region);

= /ds .(Vgs - VTO), (15)

where IDS is the drain current, calculated according to the model; lds, Vds and Vgs are experimental data; and VTO (threshold voltage), Fb (body effect factor), Beta (channel conduction factor), ETA (static feedback coefficient) and THETA (mobility degra- dation factor) are model parameters.

The above model is valid for linear and saturation regions of MOSFET operation for a transistor without narrow and short channel effects with zero bulk-potential: Vb~ = 0. The other parameters of the SPICE level three model (e.g. velocity saturation factor or channel length modulation factor) are found to correlate with five parameters of model (15). They are set to the default values to avoid redundancy.

Model (I) is close to the SPICE level three model if its parameters are fitted to minimize the difference between experimental (Ids) and calculated (IDS) values of current at all points of characteristics, thus giving the possibility of applying the values of

in space environments 1371

1.4 .-q. Irradiation Annealing PI I .

• - - V T O +

0 . 8 + - - B e t a / B e t a o v + + , 4 - + + + #

[ ] - - E T A / E T A 0 w v v

A _ F B / F B 0 w w

w - - T H E T A / T H E T A 0

0.6 . . . . . , . . . . . . . . i . . . . . . . | . . . . . . . . t •

1 0 2 1 0 3 1 0 3 1 0 4

Time, s

Fig. 3. The variation of SPICE level three model parameters for nMOSFET through irradiation and annealing. The best fit of the conversion model is shown for parameter VTO which is given in volts. The other parameters are normalized

to their pre-irradiation values.

its parameters in SPICE. This model is a three parameters first order model if j ] , J~ and f3 are treated as the variables under the control of experimenter. This fact is used for parameter extraction: the nonlinear minimization of differences between experimental and calculated data is done in the coordinate system of VTO and Fb. At each point of this system (VTOx, Fb,.) the response function is given as a residual sum of squares for fitting the model IDS (VTO = VTOx, Fb = Fby, Beta, THETA, ETA) to the set of experimental data. This least-square problem is linear and has a unique solution, thus reducing the uncertainties in parameter extraction. The physically meaningful area in the coordinate system (VTO, Fb) is not large and the response function for parameter extraction can be examined with the help of a visualization method to look for all minimums on a contour diagram. Thus, we can extract the parameters of model (15) using the global minimization algorithm in a physically meaningful area. The implementation of the method to the extraction of SPICE model parameters under irradiation and annealing is shown in Fig. 3.

6. DISCUSSION AND CONCLUSION

In this paper possible solutions are presented for problems related with the implementation of the MOSFET prediction approach, based on mathemati- cal modeling.

(1) The conversion model is suitable for expanding the results of laboratory tests to the space environ- ment, because its fitting parameters can be easily extracted from the data of irradiation/annealing experiments. It can be done due to the elimination of a formal description for the interface traps build-up [1] that results in the reduction of fitting set

1372 I. N. Shvetzov-Shilovsky

parameters. The use of the single time dependent term both for oxide trapped charge annealing, and for interface trap build-up determines the situation when any MOSFET parameter changes during irradiation and annealing according to the same time law. It gives the possibility of extracting the fitting constants for time dependent terms from the data, measuring with great accuracy (e.g. threshold voltage shift), using the dependence of time for regularization during parameters extraction, etc.

(2) The suggested form of the time dependent term is more universal with respect to linear response theory description, based on the formalism of tunneling front. As a result, it is easy to account for the influence of different factors (heating, irradiation, etc.) on annealing. Assume, for the resulting annealing time zr,~:r~ ~ = Zz~ -~, where rl are the values of annealing time due to the separate influence of different effects. Then, eqn (13) must be modified according to the analytical description of z, and this is the only modification that must be introduced to the time dependent term.

(3) The inclusion of the set of parameters by the conversion model, used in standard circuit simulation programs, gives a way to incorporate the MOSFET prediction into the circuit analysis and design. It can be done in two ways. The first consists of the application of a physical model to calculate the circuit simulation program parameters for given oxide and interface charges. Another one assumes the direct extraction of parameters from I - V curves of transistors during irradiation and annealing. The dependencies of parameters, expected according to the conversion model, are then used for improvement of accuracy of fitting results.

The presented approach of MOSFET prediction in space environments calls for future work devoted to the creation of the models, describing the tem- perature and field influence on charge build-up and annealing.

Acknowledgements--The author would like to thank Prof. Dr V. S. Pershenkov and Dr V. V. Belyakov for helpful discussions and comments. I also acknowledge the support of this work by the Specialized Electronic System, Moscow.

REFERENCES

1. Ionizing Radiation Effects in MOS Devices and Circuits, eds T. P. Ma and P. V. Dressendorfer. John Wiley, New York, 1981.

2. Galloway, K. F. and Schrimpf, R. D., MOS device degradation due to total dose ionizing radiation in natural space environment. A review. Microelectron. J., 1990, 21, 67-81.

3. Fleetwood, D. M., Winokur, P. S. and Meisenheimer, T. L., Hardness assurance for low-dose-rate space appli- cations. IEEE Trans. Nucl. Sci., 1991, 38, 1552-1556.

4. Sexton, F. W., Fleetwood, D. M., Aldridge, C. C., Garretti, G., Pelletier, J. C. and Gaona Jr, J. I., Qualifying commercial IC's for space total-dose environments. IEEE Trans. Nucl. Sci., 1992, 39, 1869-1875.

5. Khosropour, P., Fleetwood, D. M., Galloway, K. F., Schrimpf, R. D. and Calvel, P., Evaluation of a method for estimating low-dose-rate irradiation re- sponse of MOSFETs. IEEE Trans. Nucl. Sci., 1994, 41, 2560-2566.

6. MIL-STD-883D, Test Method 1019.4, Ionizing Radi- ation (Total Dose) Test Procedure. Defense Electronics Supply Center (DESC), Dayton, OH, January 1992.

7. Pershenkov, V. S., Belyakov, V. V. and Shalnov, A. V., Fast switched-bias annealing of radiation-induced oxide-trapped charge and its application for testing of radiation effects in MOS structures. 1EEE Trans. Nucl. Sci., 1994, 41, 2593-2599.

8. Khosropour, P., Galloway, K. F., Zupac, D., Schrimpf, R. D. and Calvel, P., Application of test method 1019.4 to non-hardened power MOSFETs. Proc. RADECS 93, France, 1993, pp. 300-305.

9. Stapor, W. J. and Meyers, J. P., Kinnison, J. D. and Carkuff, B. G., Low dose rate space estimates for integrated circuits using real time measurements and linear system theory. IEEE Trans. Nucl. Sci., 1993, 40, 1875-1882.

10. Fleetwood, D. M., Winokur, P. S. and Schwank, J. R., Using laboratory X-ray and cobalt-60 irradiations to predict CMOS device response in strategic and space environments. IEEE Trans. Nucl. Sci., 1988, 35, 1497-1505.

11. Schrimpf, R. D., Wahle, P. J., Andrews, R. C., Cooper, D. B. and Galloway, K. F., Dose-rate effects in the total-dose threshold-voltage shift of power MOSFETs. IEEE Trans. Nucl. Sci., 1988, 35, 1536-1540.

12. Winokur, P. S., Kerris, K. G. and Harper, L., Predicting CMOS inverter response in nuclear and space environments. IEEE Trans. Nucl. Sci., 1983, 30, 4326-4332.

13. McLean, F. B., Generic impulse response function for MOS systems and its application to linear response analysis. IEEE Trans. Nucl. Sci., 1988, 35, 1178-1185.

14. McWhorther, P. J., Miller, L. and Miller, W. M., Modeling the anneal of radiation-induced trapped holes in a varying thermal environment. IEEE Trans. Nucl. Sci., 1990, 37, 1682-1689.

15. Mondot, E. and David, J. P., Experimental procedure influence on total dose CMOS inverter hardness. Proc. RADECS 93, France, 1993, pp. 306-312.

16. David, J. P., Mondot, E., Andriamiarisoa, N. and Boyer, J. M., Large dose rate effect and rebound failure prediction in CMOS IC's. NSREC-94, Tucson, USA, 1994.

17. Lai, S. K., Interface trap generation in silicon dioxide when electrons are captured by trapped holes. J. Appl. Phys., 1983, 54, 2540-2546.

18. Pershenkov, V. S., Belyakov, V. V., Cherepko, S. V. and Shvetzov-Shilovsky, I. N., Three-point method of prediction of device response in space environment. IEEE Trans. Nucl. Sci., 1993, 40, 1714-1720.

19. Base, M. P., Plaag, R. E. and Johnston, A. H., A comparison of methods for total dose testing of bulk CMOS and CMOS/SOS devices. IEEE Trans. Nucl. Sci., 1990, 36, 1818-1824.

20. Mrstik, B. J. and Rendell, R. W., Si/SiOr--interface state generation during X-ray irradiation and during post-irradiation exposure to a hydrogen ambient. IEEE Trans. Nucl. Sci., 1991, 38, 1101-1110.

21. Lelis, A. J., Oldham, T. R. and Delancey, W. M., Response of interface traps during high-temperature anneals. IEEE Trans. Nucl. Sci., 1991, 38, 1590-1596.

22. Galloway, K. F., Gaitan, H. and Russel, T. J., A simple model for separating interface and charge effects in MOS device characteristics. 1EEE Trans. Nucl. Sci., 1984, 31, 1497-1501.

23. Draper, N. R. and Smith, H., Applied Regression Analysis. John Wiley, New York, 1981.

MOSFET prediction in space environments 1373

24. Shvetzov-Shilovsky, I. N., Cherepko, S. V. and Pershenkov, V. S., The improvement of MOSFET prediction in space environments using the conversion model. IEEE Trans. Nucl. Sci., 1994, 41, 2631-2636.

25. Oldham, T. R., Lelis, A. J. and McLean, F. B., Spatial dependence of trapped holes determined from tunneling analysis and measured annealing. IEEE Trans. Nucl. Sci., 1986, 33, 1203-1209.