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Microwave power thin film resistors for high frequency and high power load applications

October 2010
Applied Physics Letters 97(17)

October 2010
97(17)

DOI:10.1063/1.3507883

Authors:

Xin Si

Xiamen University of Technology

Wenxu Zhang

University of Electronic Science and Technology of China

Show all 6 authorsHide

The authors report a power-dividing-based microwave power thin film resistor (MPTFR) that exhibits high operating frequency and high power load. The MPTFR is comprised of substrate, ground electrodes, two TaN resistive films, power dividing circuit and signal input port. The experimental results show that the voltage standing wave ratio of the MPTFR is lower than 1.6 in the band of 3.4–7.4 GHz and 8.2–9.8 GHz. The power load of the MPTFR is 200 W. The experimental data are in good agreement with the electromagnetic simulations.

Sketch of the power-dividing MPTFR.

…

Dependences of VSWR and S 11 of the MPTFR on the frequency

…

Dependences of the impedance of the MPTFR on the frequency simulated by HFSS .

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͑ Color online ͒ Photograph of the prepared MPTFR.

…

Experimental and simulated VSWR of the MPTFR.

…

Figures - uploaded by Wenxu Zhang

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Content uploaded by Wenxu Zhang

Content may be subject to copyright.

Microwave power thin film resistors for high frequency and high power load

applications

H. C. Jiang, X. Si, W. L. Zhang, C. J. Wang, B. Peng et al.

Citation: Appl. Phys. Lett. 97, 173504 (2010); doi: 10.1063/1.3507883

View online: http://dx.doi.org/10.1063/1.3507883

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Microwave power thin ﬁlm resistors for high frequency and high power

load applications

H. C. Jiang,a兲X. Si, W. L. Zhang, C. J. Wang, B. Peng, and Y. R. Li

State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science

and Technology of China, Chengdu 610054, People’s Republic of China

共Received 23 June 2010; accepted 8 October 2010; published online 27 October 2010兲

The authors report a power-dividing-based microwave power thin ﬁlm resistor 共MPTFR兲that

exhibits high operating frequency and high power load. The MPTFR is comprised of substrate,

ground electrodes, two TaN resistive ﬁlms, power dividing circuit and signal input port. The

experimental results show that the voltage standing wave ratio of the MPTFR is lower than 1.6 in

the band of 3.4–7.4 GHz and 8.2–9.8 GHz. The power load of the MPTFR is 200 W. The

Institute of Physics.关doi:10.1063/1.3507883兴

As a power dissipation component, microwave power

thin ﬁlm resistors 共MPTFRs兲have been widely used in radar,

communication and hybrid integrated circuit, etc.1–5It is

typically used as dummy load or power-absorbent at the nor-

mally isolated ports of, such as, circulators as well as cou-

plers to absorb the extra power caused by mismatches, im-

perfect directivity, or imbalances somewhere in these

systems. By this way, the rear-end components or systems

can be avoided from being burned or destroyed.

Two main parameters of the MPTFR are operating fre-

quency and power load. With the development of radar, com-

munication and hybrid integrated circuit, etc., MPTFRs with

higher operating frequency and power load and smaller size

are required. In a single resistive ﬁlm MPTFR, the reﬂection

of the microwave power signal is described as Eq. 共1兲:6

兩⌫兩=e−0.169⌬Tk

fR␧P,共1兲

where ⌫,⌬T,k,f,R,␧, and Pare the reﬂection coefﬁcient,

the gradient of temperature of the MPTFR due to microwave

power load, coefﬁcient of heat conductivity of the substrates,

operating frequency, impedance, dielectric constant, and

power load, respectively.

From Eq. 共1兲, it is impossible to improve the operating

frequency and power load simultaneously in a single resis-

tive ﬁlm MPTFR, that is, the increase in the power load

requires larger resistive ﬁlm area, which means lower oper-

ating frequency. Accordingly, only high frequency but low

power or low frequency but high power load can be obtained

in MPTFRs with single resistive ﬁlm. In this paper, a

MPTFR based on power dividing technique was proposed

and fabricated with the aim to endow the MPTFR with high

frequency and high power load simultaneously.

Figure 1shows the structure of the MPTFR based on

power dividing. The MPTFR is comprised of substrate,

ground electrode, two resistive ﬁlms, power dividing circuit,

and microwave signal input port. The resistive ﬁlm is com-

prised of two smaller resistive ﬁlms with parallel connection.

The functions of the power dividing circuit are to divide the

input power into two parts and to match impedance. By that,

the input microwave power signal with high frequency and

high power is divided into two small equal power signal

共half of the input power兲but their frequency still equals to

the input frequency. Because the two equal microwave

power signals are dissipated at the two resistive ﬁlms, the

power load of the MPTFR is doubled with respect to those

with single resistive ﬁlm. On the other hand, the operating

frequency of the MPTFR remains unchanged due to the im-

pedance matching of the power dividing circuit.

We ﬁrst simulated the performances of the MPTFR by

HFSS software. In the simulation, BeO ceramic substrate with

the size of 20 mm⫻10 mm⫻1 mm was used as the sub-

strate of the MPTFR. TaN thin ﬁlms was used as the resistive

materials. The area of each TaN thin ﬁlm was 9 mm.2The dc

resistance of each resistive ﬁlm was 50 ⍀, so the dc resis-

tance of the overall MPTFR is 25 ⍀. Silver was used as the

electrode materials.

Figure 2shows the dependences of voltage standing

wave ratio 共VSWR兲and S11 of the MPTFR on the frequency

simulated by HFSS. It can be seen that the VSWR and S11 of

the MPTFR are lower than 1.6 and –12 dB in the band of

3–9 GHz, respectively. Figure 3shows the impedance as a

function of the frequency simulated by HFSS. From Fig. 3,

the real part of the impedance is about 50 ⍀and the imagi-

nary part is nearly zero at 5 GHz, where the S11 and the

VSWR are minimal. These results indicate that the MPTFR

can be matched to 50 ⍀at 5 GHz by the power dividing

circuit. The simulation results imply that the proposed

MPTFR based on power dividing can be applied in rf de-

vices in the band of 3–9 GHz.

a兲Electronic mail: hcjiang@uestc.edu.cn. FIG. 1. Sketch of the power-dividing MPTFR.

APPLIED PHYSICS LETTERS 97, 173504 共2010兲

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The MPTFR was fabricated by reactive magnetron sput-

tering and mask patterning technology. First, the silver elec-

trodes were fabricated by screen print technology. Then, TaN

thin ﬁlms were prepared by dc reactive magnetron sputter-

ing. A Ta wafer 共⌽60 mm with purity of 99.995 at. %兲was

used as the target. The sputtering gas is a mixture of argon

共99.99%兲and nitrogen 共99.99%兲. The nitrogen partial ﬂux

关N2/共N2+Ar兲兴 in the sputtering gas is 3%. The base vacuum

is 5⫻10−4 Pa. The distance between the target to the sub-

strate, the sputtering pressure, the sputtering time, the sub-

strate temperature and the sputtering power are ﬁxed to 80

mm, 0.2 Pa, 20 min, 600 ° C and 25 W, respectively. The

microwave performances of the sample were measured by a

vector network analyzer 共Agilent E8363C兲. The power load

was tested by applying dc power on the sample for 96 h. The

details of the testing method of microwave performances and

power load were described in Ref. 7. During the applying dc

power, the surface temperature and the dc resistance of the

sample were measured. The measurement of the temperature

coefﬁcient of resistance 共TCR兲of the resistors was described

in our previous works.8

Figure 4illustrates the photograph of the prepared

MPTFR. The results of the measurement compared with the

simulated performances are presented in Fig. 5. It can be

seen that the VSWR of the sample is lower than 1.6 across

the band of 3.4–7.4 GHz and 8.2–9.8 GHz. The minimal

VSWR is achieved at 5.8 GHz. The agreement between the

experiments and simulation is excellent. The slight differ-

ence between the measurement and the simulation can be

explained by the transition microstrip–subminiature version

A connector, which was not taken into account in the simu-

lation.

Figure 6presents experimental results of the surface

temperature and the dc resistance of the sample when it was

applied 200 W dc power. The power load experiments show

that the surface temperature of the MPTFR can be main-

tained at about 105 °C for 96 h under this power. The dc

resistance of the MPTFR can be maintained at about 25 ⍀

during this power load applying. The change in the resistance

of the sample 共⌬R/R兲is less than 1% during the power load

testing. The power density of the sample is about

10.5 W/mm2. These results indicate that the power load of

the MPTFRs is about 200 W. The TCR of the sample is about

50 ppm/°C.

In summary, we present a MPTFR based on power di-

viding technique. This MPTFR can double the power load of

the device but remain the operating frequency unchanged,

FIG. 3. Dependences of the impedance of the MPTFR on the frequency

simulated by HFSS.

FIG. 4. 共Color online兲Photograph of the prepared MPTFR.

FIG. 5. Experimental and simulated VSWR of the MPTFR.

FIG. 6. Experimental results of the surface temperature and the resistance of

the MPTFR.

FIG. 2. Dependences of VSWR and S11 of the MPTFR on the frequency

simulated by HFSS.

173504-2 Jiang et al. Appl. Phys. Lett. 97, 173504 共2010兲

Downloaded 03 Oct 2013 to 125.39.171.194. This article is copyrighted as indicated in the abstract. Reuse of AIP content is subject to the terms at: http://apl.aip.org/about/rights_and_permissions

which provides a strategy to overcome the limitation that the

operating frequency and the power load cannot be improved

simultaneously in the single resistive ﬁlm MPTFRs.

The authors would like to acknowledge the ﬁnancial

support of the Supporting Project of Sichuan 共Grant No.

2010GZ0156兲and Foundation of State Key Laboratory of

Electronic Thin Films and Integrated Devices 共Grant No.

KFJJ200804兲.

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