Conventional silicon wafers have low resistivity and consequently unacceptably high value of dielectric attenuation constant. Microwave circuits for phased array antenna systems fabricated on these wafers therefore have low efficiency. By choosing a silicon substrate with sufficiently high resistivity it is possible to make the dielectric attenuation constant of the interconnecting microwave transmission lines approach those of GaAs or InP. In order for this to be possible, the transmission lines must be characterized. In this presentation, the effective dielectric constant (epsilon sub eff) and attenuation constant (alpha) of a slotline on high resistivity (5000 to 10 000 ohm-cm) silicon wafer will be discussed. The epsilon sub eff and alpha are determined from the measured resonant frequencies and the corresponding insertion loss of a slotline ring resonator. The results for slotline will be compared with microstrip line and coplanar waveguide

Lee, Richard Q.

Simons, Rainee N.

Taub, Susan R.

Young, Paul G.

English

NASA Technical Reports Server

NASA Technical Memorandum 106058
Microwave Characterization of Slotline on
High Resistivity Silicon for Antenna
Feed Network
Rainee N. Simons
Sverdrup Technology, Inc.
Lewis Research Center Group
Brook Park, Ohio
Susan R. Taub and Richard Q. Lee
National A eronautics and Space A dmnistration
Lewis Research Center
Cleveland, Ohio
and
Paul G. Young
University of Toledo
Toledo, Ohio
(NASA-TM-I06058) MICROWAVE
CHARACTERIZATION OF SLOTLINE ON
HIGH RESISTIVITY SILICON FOR
ANTENNA FEED NETWORK (NASA) 9
G3/33
N93-27265
Unclas
0169426
Prepared for the
1992 IEEE AP-S International Symposium and URSI Radio Science Meeting
sponsored by the IEEE and USNC Commissions A, B, D, and F
Ann Arbor, Michigan, June 27-July 2, 1993
BI/ A
https://ntrs.nasa.gov/search.jsp?R=19930018076 2020-03-17T06:07:32+00:00Z

MICROWAVE CHARACTERIZATION OF SLOTLINE ON HIGH RESISTIVITY
SILICON FOR ANTENNA FEED NETWORK
Rainee N. Simons, Susan R. Taub,
Richard Q. Lee, and Paul G. Young
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135
ABSTRACT
This paper presents, the effective dielectric constant (eeff)
and attenuation constant (5) of a unshielded slotline on a high
resistivity (5000 to i0,000 _-cm) silicon wafer. The _eff (De to
40 GHz) and _ (DC to 26.5 GHz) are determined from the measured
resonant frequencies and the corresponding insertion loss of a
slotline ring resonator. The measurements are carried out at room
temperature and without the application of a DC bias. The attenua-
tion for slotline on silicon are compared with microstrip line and
coplanar waveguide on other semiconductor substrate materials.
Finally, applications of the slotline to antenna feed network are
addressed.
I. INTRODUCTION
There are several reasons why silicon is now a viable
microwave material. One reason is that silicon MOSFET's with
cutoff frequencies as high as 89 GHz have been reported (ref.l).
Another, is that silicon MMIC amplifiers, mixers and IMPATT diodes
are now commericially available (refs. 2 thru 4). The final reason
is that transmission lines, such as, microstrip line (refs. 5 thru
9) and Coplanar Waveguide (CPW) (ref. i0) with low loss have been
demonstrated on high resistivity silicon. Silicon has several
advantages over GaAs and InP technologies, such as: better thermal
conductivity, higher reliability, higher circuit complexity,
availability of wafers of very large diameters, better mechanical
properties, and lower cost (ref. 9). Furthermore, integration of
MMIC's with digital control circuits and radiating elements on a
single silicon wafer is possible. This can enhance the reliabili-
ty, efficiency and lower the cost of phased array antenna systems.
However, silicon substrates do have slightly higher dielectric loss
than traditional microwave substrates. DC bias and high operating
temperatures can increase this loss. Additional loss can be
introduced, if during processing, the wafers are exposed to
temperatures high enough to significantly lower their resistivity
(ref. 9).
Conventional silicon wafers have low resistivity and conse-
quently an unacceptably high value of dielectric attenuation.
Therefore, microwave circuits for phased array antenna systems
fabricated on these wafers have low efficiency. By choosing a
silicon substrate with sufficiently high resistivity it is possible
to make the dielectric attenuation of the interconnecting microwave
transmission lines approach those of GaAs or InP (refs. 6 and 7).
In order to fabricate microwave circuits on silicon, the
transmission lines on this material must be characterized.
Recently, the attenuation of microstrip transmission lines on high
resistivity, bare and passivated silicon as a function of frequen-
cy, temperature and DC bias have been measured (ref. 9). Also,
attenuation and _eff of CPW lines as a function of resistivity,
frequency and geometry on silicon substrates has been examined
experimentally and theoretically (ref. i0). This paper presents the
effective dielectric constant (eeff) and attenuation constant (a)
of an unshielded slotline on a high resistivity (5000 to i0,000 _-
cm) silicon wafer over the frequency ranges DC to 40 GHz and DC to
26.5 GHz respectively. The measurements are carried out at room
temperature and without the application of a DC bias.
II. THEORY
An experimental slotline ring resonator is shown in figure i.
The advantage of a ring resonator over a series gap coupled linear
resonator is that the ring resonator is free of end effects. The
loaded Q-factor, QL, of the resonator is determined from the
following equation relating the measured resonance frequency, f0,
and the frequency range, _f, between the 3-dB points on either
side of the resonance:
QL = fo / Af. (1)
The unloaded Q-factor, Qu, of the resonator is determined from the
following equation relating the measured peak insertion loss, L, at
resonance and QL:
L (dB) = 20 Log {I [QL/Qu]}- (2)
The Seff is determined from the following equation:
6eff = (30 n/f 0 1) 2 (3)
Where n is an integer and denotes the order of resonance. Therefore
for n resonances of a particular resonator, n values of _eff can be
obtained. 1 is the mean circumference of the ring in cm. f0 is in
GHz.
The phase velocity, Vph,
slotline is equal to
of the electromagnetic wave on the
Vph = 3x108 /IEef f (mt/sec). (4)
Finally, the attenuation constant a of the slotline is determined
from the relation:
(_ = 7[ f0 /Qu Vph (Np/mt) . (5)
iII. RESONATOR FABRICATION AND EXPERIMENTAL RESULTS
The slotline ring resonator is fabricated on a silicon wafer
which is coated sequentially with 700 A of silicon dioxide, 200
of chromium and 2.5 _m of gold. The thickness, T, of the gold
metalization is greater than three times the skin depth at 8.5 GHz
and above. The measured resistivity of the silicon dioxide layer is
1014 _-cm. The eeff and _ are determined by substituting the
measured resonant frequencies and the corresponding insertion loss
in equations i thru 5. Figure 2 presents the geff as a function of
the frequency. In this figure the slot width W, wafer thickness D,
and relative dielectric constant ar, are equal to 0.i mm, 0.381 mm
and 11.7, respectively. Also shown in Fig.2 is the computed geff
which is obtained as described in ref.ll. The measured and computed
6ef f are in good agreement.
The intrinsic peak insertion loss L of the resonator is
corrected for the insertion loss due to the microstrip feed lines
and the coaxial connectors of the fixture. This is done by
subtracting the feed and connector loss from the overall measured
insertion loss. These excess losses are determined from a separate
set of measurements using a thru line of length equal to the sum of
the feed line lengths in the test fixture. Figure 3 presents the
measured attenuation _ as a function of the frequency. The W, D and
_r of the slotline are the same as those in Fig. 2. The attenuation
of slotline is compared in Table i with the measured results from
the open literature for microstrip line and coplanar waveguide on
various other semiconductor substrate materials. It is worth
mentioning here that the attenuation values quoted in Table 1
depend on the substrate thickness, metalization thickness and also
the strip conductor width and/or slot width which are not the same
in all cases.
IV. CONCLUSIONS AND DISCUSSIONS
The geff and _ for a slotline on a high resistivity silicon
substrate have been experimentally obtained. The attenuation
constant for slotline has been compared with that of microstrip
line and coplanar waveguide on other semiconductor substrate
materials. The value of attenuation for slotline was found to be
comparable to other transmission lines. This, however, can only be
a rough comparison because attenuation depends upon the substrate
thickness, metalization thickness and strip conductor width and/or
slot width which are not the same in all the cases. However our
experiments demonstrate the viability of high resistivity silicon
for low loss antenna feed network. Application of this information
to the feed network will be presented at the symposium.
i ,
•
•
•
5.
•
7 •
,
•
i0.
ii.
12.
13.
REFERENCES
Yan, R.H., et al.: 89-GHz fT Room-Temperature Silicon
MOSFET's, IEEE Electron Device Letters, Vol. 13, No. 5, pp.
256-258, May 1992.
Hanes, M.H., et al.: MICROX TM -An All-Silicon Technology for
Monolithic Microwave Integrated Circuits, IEEE Electron
Device Letters, Vol. 14, No.5, pp. 219-221, May 1993.
Hewlett Packard Communications Components, GaAs and Silicon,
Designers Catalogue, Section 8, 1993.
Hughes millimeter Wave Products Catalogue.
Hyltin, T.M.: Microstrip Transmission on Semiconductor
Dielectrics, IEEE Trans. Microwave Theory Tech., VoI.MTT-13,
No.6, pp.777-781, Nov. 1965.
Young, L. and H. Sobel (Editors), Advances in Microwaves,
Vol.8, Academic Press, New York, New York, 1974, pp. 19-25.
Rosen, A., et al.: Silicon as a Millimeter-Wave Monolithica-
lly Integrated Substrate - A New Look, RCA Rev., Vol. 42,
pp. 633-660, 1981.
Caviglia, A.L. et al.: Microwave Performance of SOI n-
MOSFET's and Coplanar Waveguides, IEEE Electron Device
Letters, Vol.12, No.l, pp.26-27, Jan. 1991.
Levesque, K., et al.: Microwave Characterization of High
Resistivity Silicon, Microwave Hybrid Circuits Conf., Oct.
1992.
Taub, S.R. and P.G. Young: Attenuation and geff of Coplanar
Waveguide Transmission Lines on Silicon Substrates, Eleventh
Annual Benjamin Franklin Symposium on Antenna and Microwave
Technology in the 1990s Digest, pp.8-11, May 1993.
Simons, R,N.: Suspended Slot Line Using Double Layer Dielec-
tric, IEEE Trans. Microwave Theory Tech., Vol. MTT-29, No.
i0, pp.l102-1107, 0ct.1981.
Higgins J.A.: Microwave GaAs FET Monolithic Circuits, 1979
IEEE Inter• Solid-State Circuits Conf. Digest of Tech.
Papers, pp. 120-121.
Haydl, W.H. et al.: Millimeterwave Coplanar Transmission
Lines on Gallium Arsenide, Indium Phosphide and Quartz with
Finite Metalization Thickness, 1991 IEEE MTT-S Inter• Micro-
wave Symp. Digest, pp. 691-694, 1991.
14. Haydl, W.H.,: Experimentally Observed Frequency Variation of
the Attenuation of Millimeter-Wave Coplanar Transmission
Lines with Thin Metalization, IEEE Microwave & Guided Wave
Letters, Vol.2, No.8, pp.322-324, Aug. 1992.
5
TABLE 1
Comparision of Attenuation Constant of Microwave Transmission
Lines on Semiconductor Substrates
TRANSMISSION LINE
Microstrip
(z0 = 50 _)
Coplanar waveguide
(CPW)
(Zo = 50 _)
Coplanar Waveguide
(CPW) l
(Z 0 _ 35 _)
Coplanar Waveguide
(CPW)
(zo = 5o _)
Microstrip
(Z o = 50 _)
Microstrip
(Z o = 50 _)
Coplanar waveguide
(CPW) 2
(zo = 5o _)
Coplanar waveguide
(cpw)2
(Z 0 = 60 _)
Slotline 2
(zo = 6o _)
SUBSTRATE
MATERIAL
SI GaAs
SI GaAs
SI InP
SI GaAs
High Res.
silicon (1.5
k _-cm)
High Res.
Silicon (8 k
_-cm)
High Res.
Silicon (2.5
3.3 k_-
cm)
High Res.
Silicon (4 k
_- cm)
High Res.
Silicon (5
i0 k _-cm)
DIMENSIONS
(Inch)
D = 0.025
W = 0.025
T = 3 _m*
D = 0.025
S = 0.025
W = 0.0125
T = 3 _m*
D= 0.5 mm
S = 88 _m
W = 16 _m
T = 0.25 9m*
D= 0.5 mm
S = 75 ;Jm
W= 56 _m
T = 3 _J/n*
D = 0.01
W = 0. 0065
D = 0.021
W = 0. 016
T _ 3 _Un
D = 0.0O8
S = 0.0O4
W = 0.002
T = 2.5 _m*
D = 400 _m
S = 30 Nm
W= 35 _m
T 1 _m $
D = 0. 015
W = 0.004
T = 2.5 _m*
ATTENUATI ON
@ i0 GHz
(dB/cm) _
0.105
0.16
4.5
0.45
0.5
0.16
0.62
0.25
REFERENCE
12
12
14
13
5
i0
This work
D is suDstrate thlckness and T is metallzat_on thickness
Microstrip: W is strip width
Coplanar Waveguide: S is center strip width and w is slot width
IMetal thickness less than one skin depth
2A SiO_ interfacial layer is present
e _ $ . ,Gold conductors, Aluminium conductors
T_L _L
I [ ,, IT
/ /
/ R=1.00584cm ---_ Ls _--
C°Cr--' W m = 0.01016 cm
Ls = 0.09271 cm
T = 2.5 pJ11
_sr = 11.7
Figure 1 .---Slotline ring resonator electrornagneticaJly coupled to
microstrip feed lines.
"°i>__,- ¢j
8 I-- O Measured _ u_" .4
| - Computed[9] __
6 0 O0 ,_
2 00 10 2O 30 40
Frequency, GHz
Figure 2.--Effective dielectric constant.
O
o
L 1
10 20
Frequency, GHz
Figure 3.--Attenuation constant.
I
3O
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4. TITLE AND SUBTITLE 5. FUNDING NUMBERS
Microwave Characterization of Slotline on High Resistivity Silicon for
Antenna Feed Network
6. AUTHOR(S)
Rainee N. Simons, Susan R. Taub, Richard Q. Lee, and Paul G. Young
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135-3191
9. SPONSORING/MONITORING AGENCY NAMES(S) AND ADDRESS(ES)
National Aeronautics and Space Administration
Washington, D.C. 20546-0001
WU-506--44-2C
8. PERFORMING ORGANIZATION
REPORT NUMBER
E-7659
10. SPONSORING/MONITORING
AGENCY REPORT NUMBER
NASA TM- 106058
11. SUPPLEMENTARY NOTES
Prepared for the 1993 IEEE AP-S International Symposium and URSI Radio Science Meeting sponsored by the IEEE and USNC Commissions
A,B,D, and F, Ann Arbor, Michigan, June 27-- July 2, 1993. Rainee N. Simons, Sverdmp Technology, Inc., Lewis Research Center Group, 2001
Aerospace Parkway, Brook Park, Ohio 44142; Susan R. Taub and Richard Q. Lee, Lewis Research Center; and Paul G. Young, University of
Toledo, Toledo r Ohio 43606. Responsible person, Rainee N. Simons, (216) 433--3462.
12l. DISTHIB_N/AVAILABILrrY STATEMENT 12b. DISTRIBUTION CODE
Unclassified - Unlimited
Subject Category 33
13. ABSTRACT (Maximum 200 words)
Conventional silicon wafers have low resistivity and consequently unacceptably high value of dielectric attenuation
constant. Microwave circuits for phased array antenna systems fabricated on these wafers therefore have low efficiency.
By choosing a silicon substrate with sufficiently high resistivity it is possible to make the dielectric attenuation constant
of the interconnecting microwave transmission lines approach those of GaAs or InP. In order for this to be possible, the
transmission lines must be characterized. In this presentation, the effective dielectric constant (Eeff) and attenuation
constant (ct) ofa slotline on high resistivity (5000 to 10 000 I)-cm) silicon wafer will be discussed. The eeff and (x are
determined from the measured resonant frequencies and the corresponding insertion loss of a slotline ring resonator. The
results for slotline will be compared with microstrip line and coplanar waveguide.
14. SUBJECT TERMS
High resistivity silicon; Slotline; Effective dielectric constant, Attenuation
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