2010 Asia-Pacific International Symposium on Electromagnetic Compatibility, April 12 -16,2010, Beijing, China

Rep-Rate Influence on Electromagnetic Effects Libor Palisek1, Lubos Suehl

VOP-026 Sternberk, s.p., division VTUPV Vyskov,

V. Nejedleho 691,68201 Vyskov, Czech Republic

ll.palisek@vtupv.cz

21.suchy@vtupv.cz

Abstract- Some results obtained during experimental measurements of susceptibility of electronics to HPM and UWB irradiation with repetition rate signals are presented in this paper. Repetition rate dependence is considered for temporary

failures as well as for damage levels too. As equipments under test are chosen regular PC setups. Simple electronic circuit are added for some experiments for possibility to achieve more results related to damage levels.

Suitable simplified circuit models for HPM and UWB repetition rate effectiveness for achieving of typical effects on electronics is used for simulations. For this purpose model based on electro­thermal analogy is used within the software OrCAD 15.7 (PSpice

model) environment. Results from measurements are compared with results from simulations. At the end of this presentation recommendation for

effective HPM and UWB rep-rate necessary to achieve typical

failures of tested equipments is carried out.

I. INTRODUCTION

Pulse power electromagnetic fields like NEMP (Nuclear Electromagnetic Pulse), HPM (High Power Microwave) and UWB (Ultra-wide Band) are considered as a possible threat for sensitive electronic equipments [1]. While NEMP is considered as a typical single pulse threat, HPM and UWB are often considered as signals with possibility of repetition rates according to state of the art technologies. HPM and UWB signals are mentioned and compared with other electromagnetic threats in Fig. 1.

- 10-1

Spectral density

(V/m)/Hz

1--____.. LightningC)

1/w

EMI Environment b)

\

Narrowbanda) Range dependent

(e.g. HPM, HIRF, etc.)

Wideband (UWB) 1/00

Range dependent

1/�"- -- .- .»-

-10 kHz -1 MHz -10 MHz -300 MHz -1-10 GHz

Frequency Hz

a) Narrow band extending from -0,2 to -5 GHz b) Not necessarily HPEM c) Significant spectral components up to -10 MHz depending on range and application

lEe 1531104

II. RESULTS FROM MEASUREMENTS

Measurements related to electromagnetic immunity to HPM and UWB signals were carried out in the past. Influence of rep-rate was studied. First of all results from UWB measurements will be mentioned and after that results from HPM testing will be discussed too.

A. Results from UWB testing

UWB signal with rise time 0 .5 ns (10% - 90 % of amplitude) and duration 2 ns was used to irradiate tested setups. One of used setups is shown in Fig. 2. Results from testing related to UWB rep-rate influence are shown in Fig. 3 and Fig. 4.

Fig. 2 Communication over UTP irradiated by UWB

100

90

80

� 70

e.:. '" 60 '"

.Q 50 a; -" 40 u '" 0.. 30

20

10

0

-I--I---

---

1 pulse

-

-

-

-

-

-

-

-

-

150 pulses (50 Hz) 300 pulses (100 Hz)

Fig. 1 HPM and UWB comparison with other electromagnetic threats [2] Fig. 3 UTP 2 m irradiated by UWB

978-1-4244-5623-9/10/$26.00 ©2010 IEEE 146

SN74ALSOOAN

0,9

0,8

0,7

0,6

0,5 � . 0 0,4

0,3

0,2

0,1

single puis 2 pulses (10 Hz) 30 pulses (10 Hz)

Fig. 4 SN74ALS in simple circuit, single pulse influence vs. rep-rate, UWB testing, A - normal performance, D - damage

From previous pictures (see Fig. 3 and Fig. 4) it is obvious UWB rep-rate influence was observed only for temporary failures (like communication distortion) but for damage level failures almost no influence of UWB rep-rate was observed

B. Resultsfrom HPMtesting

RPM signal with frequency 9.3 GRz was used to irradiate tested setups. Duration of the pulse (pulse width) was 0 .5 IlS, rep-rate was changed up to 2 kHz. Results from testing related to RPM rep-rate influence are shown in Fig. 5.

0,9

0.8

0,7

� 0,6

� 0.5

g w 0,4

0,3

0.2

0.1

single pulse 10 100 1000

Rep-rate frequency (Hz]

2000

I-A1 �

Fig. 5 PC temporary failures, single pulse influence vs. rep-rate, HPM 9 GHz, pulse width 0.5 Ils, A - normal performance, C - temporary failure

From Fig. 5 it is obvious RPM rep-rate influence was quite low for studied temporary failures.

From both UWB testing as well as RPM testing influence of rep-rate was observed for temporary failures. For damage levels almost no influence was observed. It is possible to consider influence of used rep-rates like a statistical effect. Achievable rep-rates with used UWB and RPM generators up to 2 kHz seemed to be too low to cause "cumulative" effects to disturb electronic. It was the reason to make suitable model for rep-rate influence investigations where rep-rate could be increased arbitrarily.

III. MODEL OF REp-RATE INFLUENCE IN ELECTRONIC

STRUCTURES

It is known the most vulnerable parts of electronic are semiconductors. Due to this fact the area of interest was focused on semiconductor junction. The principle mechanisms by which a semiconductor junction may fail are surface breakdown and internal breakdown through the junction within the body of the device [3 ], [4]. Main problem within the junction is an internal breakdown where destruct mechanism results from changes in the junction parameters due to the high temperatures locally within the junction area. This mechanism is valid even for very short pulses (ns) [5]. Very high temperatures of junction lead to melting or even evaporation of the junction (�1000 0c). For this consideration suitable temperature model of the junction would be useful. Electro-thermal analogy was used for the purpose to simulate rep-rate influence within the semiconductor junction.

In general electric circuits as well as thermal circuits can be described by differential equations. Electric circuit analyses programs offer required solutions by means of fmite element analysis techniques [6]. If suitable analysis program for electric circuits is available it is useful to transfer thermal circuit to electrical one and to provide relevant simulation in analyses program environment. For our case we used program arC AD 15.7 (PSpice model).

First of all it is necessary to identify the correspondence between electrical and thermal parameters and variables. For the thermal mass it is usual to use capacitance as an analog. Other possibility would be to use inductance instead of capacitance. In our case when capacitance is used in model electric current represents power flow and the voltage represents temperature [6]. This analogy can be explained by next equations:

TM(t) = TM(O)+ f � dt

where: TM is temperature of thermal mass, °C P is power input to thermal mass, W M is thermal mass (thermal capacitance), JrC VC is voltage on capacitance, V i is current input to capacitance, A C is value of capacitance, F

(1)

(2)

Comparing the equations (I) and (2) we fmd that temperature corresponds to voltage, power (thermal) corresponds to current and thermal mass (thermal capacitance) corresponds to electrical capacitance. Since current is the analog of power (thermal) then an electrical current source can be analog of heat power source. A resistor in an electrical circuit corresponds to thermal resistance.

Model of transistor as an example was used for our simulations. For this purpose 6 stage RC network was created

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(see Fig. 7) in OrCAD 15.7 environment. It was necessary to find relevant parameters for this RC network, thermal resistances and thermal capacitances. These parameters were gained from [7]). Relevant parameters can be in principle gained by measurement or by calculation. Transistor structure (see Fig. 6, [7]) was used like a good example of semiconductor structure with relevant parameters of thermal resistances and thermal capacitances.

Metalization

Bottom layer 5

I Heat

: Extraction

t

Silicon Die layer 1

Fig. 6 Thermal layers in the IXYS RF MOSFET [7]

11

TO = On

TF = 5n

PW = {1n·w}

PER = {1/reprate}

11 = 0

12 = 10k

TR = Sn

PARAMETERS:

R1 R2 R3 R4 R5 0.103 0.047 0.012 0.15 9.ge-3

�o

Fig. 7 6 stage RC network

R6 C6 0.205 2e-5

Various simulation profiles were defined for 6 stage network shown in Fig. 7. Rectangular current pulse was used as a source (see Fig. 7) . The pulse length was changed from 1 ns up to 1 ms. Single pulse influence was compared with rep­rate up to MHz region. As it was mentioned above according to electro-thermal analogy the power (thermal) is presented by current source (see Fig. 7) , thermal capacitances of transistor structure are presented by electrical capacitances C 1 - C6 and thermal resistances within the transistor structure are presented by resistors Rl - R6. The voltages measured within the RC network (see Fig. 7) represent temperatures within the transistor structure. For our example 6 layers according to Fig. 6 were considered and it led to 6 stage network (see Fig. 7) and 6 relevant voltages representing 6 temperatures within the transistor structure were calculated in program OrCAD 15.7. Absolute values of voltages (representing temperatures) were not very important for our considerations related to rep-rate influence. For our case the value of current source (amplitude) was set to 10 kA which creates voltages up to few kV within the simulated structure (see Fig. 7) . The relationship 1 V = 1 °C can be set for the model. Normalized values would be sufficient as well to be able to evaluate influence of rep-rate on temperature effects within the semiconductor structure.

First basic results from simulation related to 6 stage model shown in Fig. 7 are presented in next Fig. 8 and Fig. 9. Temperatures within the structure of the model are shown in colors according to markers in Fig. 7. From these pictures it is obvious for short pulses (100's ns) can be increasing of temperature of semiconductor junction (see Fig. 8, green curve) considered like an adiabatic state where the delivered energy is completely stored and transferred to temperature. Here the destruction level is proportional to the delivered energy - proportional to the product of pulse power and pulse time [5]. For very long pulses (see Fig. 9) there exists temperature (voltage in our model) which is not increased with increasing the pulse length. Pulses with duration 100's lis are long enough to achieve this maximum temperature (see Fig. 9). For pulses with length few lis there is a region which is often called Wunsch-Bell region [5] where destruction energy is considered like proportional to the square root of the pulse length.

Fig. 8 Output voltages (temperatures) for 100 ns pulse

.. t.!... 1._ o _1.1t,1, -I(U,') ' -'(.l'�1 -IC'.") ·ICI'''!) -1(11'1':1

Fig. 9 Output voltages (temperatures) for I ms pulse

After "first basic" simulations (see previous paragraph) simulation profiles with rep-rate or pulse length as a parameter were defined and "only" temperature of the silicon die was studied within the proposed 6 stage model (see Fig. 10 - Fig. 12).

From Fig. 10 it is obvious for considered short pulses (ns region) rep-rates lower than 1 MHz are not effective to achieve higher temperatures of silicon die to make relevant effects. For longer pulses, lower rep-rates can be used to achieve higher temperatures of silicon die, for example rep­rates 100's kHz can have an effects for pulses with length 1 lis (see Fig. 11). This behavior corresponds with duty cycle of used signal. Very important parameter is a time constant L for discharging capacitance Cl (see Fig. 7) to other stages of RC

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network from silicon die to other layers of transistor model. This time constant (r) can be considered close to 1 fls for our model. It means rep-rate should be higher than approximately 11 't to achieve "cumulative" effect - increase of silicon die temperature. Fig. 12 shows high increase of silicon die temperature for pulses from I ns to I fls. From this picture it is obvious there is high influence of pulse width on silicon die temperature. Comparisons of Fig. 10 - Fig. 12 lead to conclusion it is much more effective to increase the pulse length and use this signal like a single shot rather than to use pulses with shorter length with rep-rate possibility. In this case depending on the structure very high (ca 1 MHz) rep-rates can be necessary to achieve cumulative effects - increasing of temperature of silicon die and to cause damage of silicon structure.

Fig. 10 Output voltage (temperature) for 2 ns pulses, rep-rate = 1 MHz, 10 MHz, 30 MHz

heat flow circuit. Simulation was carried out for the purpose to find influence of rep-rate on electromagnetic effects considering overheating of semiconductor structures (silicon die). Used model allowed investigating rep-rate influence in wide range. Rep-rate could be changed arbitrarily.

From simulations it was obvious rep-rate of considered signals like HPM or UWB should be very high for considered transistor structure (higher than 1 MHz) to achieve "cumulative" effects to increase the temperature of considered silicon structure. As more suitable way to achieve higher temperatures within the semiconductor structure it was recommended to increase the pulse length rather than to use rep-rate signals.

Before simulations some experiments related to rep-rate influence were carried out. Unfortunately rep-rates of signals generated with used generators were very low (up to 2 kHz) so almost no influence on effects on electronic was observed. Only for some temporary failures (like communication distortion) can be low rep-rates effective and useful.

With proposed model using circuit simulation program it was possible to fmd influence of rep-rates on electromagnetic effects caused due to semiconductor structure overheating which is typical for damage level failures.

ACKNOWLEDGMENT

This work was supported by Ministry of Defence, Czech Republic (The project "Defence capabilities against DEW -Vulnerability assessment of weapon systems and infrastructure C2, OSPROZ-DEWI ").

REFERENCES

[1] TAYLOR, C. D., GIRl, D. V. High-Power Microwave Systems and Effects. Washington: Taylor and Francis, 1994. 199 p. ISBN 1-56032-302-7.

[2] IEC 61000-2-13: 2005, Electromagnetic compatibility (EMC) - Part 2-13: Environment - High-power electromagnetic (HPEM) environments - Radiated and conducted.

Fig. 11 Output voltage (temperature) for 1 us pulses, rep-rate = 10 kHz, 100 [3] D. C. Wunsch, R. R. Bell, "Determination of threshold failure levels of semiconductor diodes and transistors due to pulse voltage," IEEE Trans. Nuc. Sci. NS-15, Dec. 1968, pp. 244-259.

kHz, 500 kHz, 1 MHz

Fig. 12 Output voltage (temperature) for pulses 1 ns, 10 ns, 100 ns, 1000 ns (single pulse incidence)

IV. CONCLUSIONS

It was shown electric circuit simulation program can be very useful tool to analyze the transient thermal response of

[4] D. M. Tasca, "Pulse power failure modes in semiconductors," IEEE Trans. Nuc. Sci. NS-17, 1970, pp. 364-372.

[5] 1. Bohl "HPM Interaction with Electronics, Skript and Presentations" High-Power Electromagnetics Course HPE 201-2007, Bonascre, France, 2007.

[6] 1. O'Loughlin, D. Loree, "Cooling system transient analysis using an electric circuit program analog", in Digest of Technical Papers, IEEE Catalog Number 03CH37472, 2003, pp. 767 - 770.

[7] IXYS RF Thermal Resistance and Power Dissipation. IXYS RF [online]. 2003. [cited 2009-09-21]. Available from: <http://www.ixysrf.com/pdflswitch _ mode/appnotes/l aprtheta ""power_ dissipation.pdf>.

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