Microfabrication of Linear Translator Tuning Elements in Submillimeter-Wave Integrated Circuits - Microelectromechanical Systems, Journal of

404

JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 7, NO. 4, DECEMBER 1998

Microfabrication of Linear Translator Tuning

Elements in Submillimeter-Wave Integrated Circuits

Victor M. Lubecke,

Senior Member, IEEE,

William R. McGrath,

Member, IEEE,

Yu-Chong Tai, and David B. Rutledge,

Fellow, IEEE

Abstract—

A micromechanical planar tuning element has been

developed and demonstrated in a fully monolithic 620-GHz in-

tegrated circuit. It allows for the mechanical variation of the

electrical length of a coplanar transmission line tuner and is

called a

sliding planar backshort

(SPB). It consists of a movable

patterned rectangular metal plate confined by polyimide flanges

along two of its edges to allow guided linear translation along the

length of a dielectric-coated coplanar transmission line. Its fab-

rication involves an application of sacrificial-layer and molding

techniques to materials and processes which are compatible with

the fabrication of a wide range of submillimeter-wave integrated

circuits. This is the first reported micromechanically adjustable

tuning element demonstrated at submillimeter wavelengths. [319]

Index Terms—

Backshort, coplanar, MEMS, micromachining,

millimeter wave, monolithic integrated circuit, planar tuning

element, submillimeter wave.

I. I

NTRODUCTION

ICROMACHINING techniques offer great potential to

millimeter- and submillimeter-wave circuit technology.

Critical dimensions in these circuits decrease with increasing

operating frequency, creating fabrication difficulties which

can be addressed through micromachining. Additionally, mi-

cromachining techniques and micromechanical components

can allow for the development of new unconventional high-

frequency circuitry which can offer superior performance.

Silicon

bulk micromachining

techniques have already been

demonstrated in submillimeter- and near-submillimeter-wave

circuits. Reflecting cavities for membrane-supported planar

submillimeter-wave antennas have been fabricated by stacking

anisotropically etched silicon wafers [1]. A similar selective

etching technique has also been employed to create wave-

guide sections in silicon, incorporating internally suspended

membranes which can allow for the integration of planar

high-frequency devices [2]. Bulk techniques have also been

Manuscript received December 29, 1997; revised August 3, 1998. This

work was supported in part by the Innovative Science and Technology Office

of the Ballistic Missile Defense Organization, Office of Space Science and

Technology, National Aeronautics and Space Administration (NASA), and a

NASA GSRP Fellowship. Subject Editor, N. de Rooij.

V. M. Lubecke was with the Division of Engineering and Applied Science,

California Institute of Technology, Pasadena, CA 91125 USA. He is now

with the Photodynamics Research Center, Institute of Physical and Chemical

Research (RIKEN), Sendai 980, Japan (e-mail: victor@postman.riken.co.jp).

Y.-C. Tai and D. B. Rutledge are with the Division of Engineering and

Applied Science, California Institute of Technology, Pasadena, CA 91125

USA.

W. R. McGrath is with the Center for Space Microelectronics Technology,

Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA

91109 USA.

Publisher Item Identifier S 1057-7157(98)08920-3.

used to selectively remove substrate material from critical

regions in planar high-frequency transmission line compo-

nents in order to reduce losses and enhance isolation [3].

Silicon

surface micromachining

techniques offer potential in

this field as well, as they have been used to create various

submillimeter-scale rotating and translating structures [4] on

which mechanically adjustable submillimeter-wave compo-

nents can be based. Techniques similar to those demonstrated

in simplified LIGA-like processes [5] can potentially make

surface micromachining techniques practical in a variety of

conventional high-frequency circuits.

At millimeter and submillimeter wavelengths, the perfor-

mance of common semiconducting and superconducting de-

vices is severely degraded by the effects of parasitic reactances

inherent in their geometries [6], [7]. These effects are not easily

characterized, and adjustable impedance matching circuits are

typically needed to make practical use of such devices. A

common approach is to embed the device in a waveguide

circuit and employ mechanically adjustable waveguide back-

shorts as tuning elements which serve to optimize the device

performance by compensating for the parasitic reactance [8].

The critical dimensions for these circuits are very small,

decreasing in size as the frequency of interest increases. This

makes fabrication of such waveguide circuits exceedingly

costly and difficult and has motivated interest in alternative

planar approaches.

Monolithic integrated-circuit technology promises a prac-

tical means for realizing reliable and reproducible planar

millimeter- and submillimeter-wave circuits. Planar circuits are

fabricated through photolithographic techniques, which allow

for the cost-effective production of intricate designs not possi-

ble with waveguide technology. These circuits, however, must

also provide compensation for parasitic device reactances.

Conventional planar technology allows for only fixed tuning

elements, providing no means for postfabrication optimiza-

tion of performance [9]. This makes characterization of the

component elements critical, and it is not usually possible

to achieve satisfactory results without multiple design and

fabrication iterations. It would be desirable to incorporate in

these planar circuits the same kind of mechanically adjustable

tuning available in waveguide circuits.

An adjustable planar tuning element, which functions in a

planar circuit analogously to a backshort in a waveguide cir-

cuit, has been developed along with a process for its fabrication

as an integral part of a millimeter- or submillimeter-wave

monolithic circuit. This is the first reported demonstration

of an integrated micromechanically adjustable tuning element

1057–7157/98$10.00



1998 IEEE

LUBECKE

et al

.: MICROFABRICATION OF LINEAR TRANSLATOR TUNING ELEMENTS

405

Fig. 1. Conceptual illustration of an SPB tuning element. A patterned metal

plate slides over a dielectric-coated planar transmission line to vary the

electrical length.

at submillimeter wavelengths. The tuning element, called a

sliding planar backshort

(SPB), is formed as an integral

part of a coplanar transmission line tuning stub, using only

conventional micron-scale fabrication techniques commonly

employed for submillimeter-wave circuits, which include UV

lithography, evaporated and electroplated metals, and sputtered

and spun-on dielectrics. The SPB can be used in developmental

integrated circuits as an aid for device characterization or

as a means to optimize in-use performance for a variety of

submillimeter-wave integrated circuits.

II. I

NTEGRATED

SPB’s

An SPB consists of a rectangular metal plate, with ap-

propriately sized and spaced holes, which rests on top of a

dielectric-coated planar transmission line, as shown in Fig. 1.

The impedance of the sections of line covered by metal is

greatly reduced, while the uncovered sections retain their

higher impedance. Each of these sections is approximately one

quarter of a wavelength long, and the cascade of alternating

low- and high-impedance sections results in an extremely low-

impedance termination. This termination can be moved to vary

the electrical length of a planar transmission line tuning stub

by simply sliding the metal plate along the length of the line.

Such adjustable tuning stubs can be used in a variety of ways

to adjust the impedance match between the various elements

of a circuit [10]. The semiempirical design of the SPB was

originally carried out with a 2-GHz-scale model [11], and SPB

tuners have since been successfully demonstrated as discrete

components at frequencies up to 100 GHz [12].

The wavelength for a signal guided on a planar transmission

line is determined by the frequency of the signal and the

dielectric properties of the substrate, decreasing in size with

increasing frequency and dielectric constant [13]. Since an

SPB tuner works as a distributed transmission line component,

its dimensions vary accordingly. At low frequencies, these

dimensions are large by micromachining standards, even for

substrate materials with relatively high-dielectric constants

like silicon. At frequencies above 100 GHz, however, the

dimensions can be on the order of hundreds or tens of microns.

At 620 GHz, an SPB on a silicon dioxide substrate can be

about 200

m wide, comparable in size to linear translating

structures fabricated through the surface micromachining of

silicon [4]. Unfortunately, the processes and materials typ-

ically used for such structures can be inappropriate for, or

incompatible with, those often needed in submillimeter-wave

circuit fabrication.

Micromachining with polysilicon components and silicon

dioxide sacrificial layers typically requires high-temperature

chemical vapor deposition (CVD) or furnace growth and

aggressive and hazardous chemical etchants. Many conven-

tional submillimeter-wave circuits, containing delicate thin-

film structures, diodes, and other devices, cannot easily accom-

modate such processes. It is desirable that the sliding element

of an SPB tuner be made from a good conductor through a

process which involves temperatures and reactions which can

be safely used on a wide range of insulating substrates which

already contain thin-film circuitry. Fortunately, key features

from the silicon-based technique can be suitably combined

with an LIGA-like UV process to allow for the fabrication

of SPB tuners in a variety of submillimeter-wave circuit

applications, using only rudimentary fabrication facilities and

very low-hazard materials and processes [14].

An all-monolithic quasi-optical 620-GHz direct-detection

circuit was developed to demonstrate the operation of inte-

grated submillimeter-wave SPB tuners. This circuit uses a

dielectric-filled parabola [15] substrate lens to focus radiation

onto a slot antenna and couples this radiation to a detector

by means of two coplanar waveguide (CPW) transmission

lines, each with integrated SPB tuners. One SPB tuner creates

a variable reactance in series between the antenna and the

detector, potentially serving to compensate for any unwanted

reactance when the slot is not resonant. The other SPB tuner

creates a variable susceptance in parallel with the detector

and could be used to compensate for the parasitic capaci-

tance found in some otherwise desirable submillimeter-wave

devices. The entire circuit can be fabricated through simple

processes commonly employed in the making of millimeter-

and submillimeter-wave integrated circuits.

III. S

UBMILLIMETER

-W

AV E

IRCUIT

ABRICATION

Submillimeter-wave circuits are made with a variety of low-

loss dielectric substrates, high-speed semiconductor devices,

and even superconducting thin films. The choices depend on

the applications, and components which are not restricted to

one medium or process are desirable.

Except for the SPB tuners, the 620-GHz detector circuit

used here is conventional; it incorporates materials, com-

ponents, and fabrication processes common to many fixed-

tuned submillimeter-wave circuits. Fused quartz was used

for the substrate lens, which provides low-loss transmission

line properties and a reasonable match to free space. The

transmission line and antenna circuitry were straightforward

thin-film patterns, and a patterned thin film of bismuth was

used as a thermoelectric detector [16]. While this type of

detector does not provide the sensitivity of semiconducting

and superconducting mixing elements, it offers the advan-

406

JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 7, NO. 4, DECEMBER 1998

Fig. 2. Exploded illustration of the seven-layer circuit. Two SPB tuners were included using conventional submillimeter-wave circuit fabrication

techniques.

tage of working at room temperature, with only a single

layer of processing. Techniques are available, however, for

integrating gallium arsenide Schottky diodes, superconduc-

tor–insulator–superconductor (SIS) junctions, and similar de-

vices in this circuit [17], [18]. The completed circuit required

seven masks and seven processing layers, and the process is

illustrated in Fig. 2.

The entire circuit was fabricated at the center of a round

254-

m-thick 19-mm-diameter fused-quartz wafer which

could be seamlessly installed on a quartz lens. The first

process layer consisted of 1000

A of gold, with 70-

m chrome

adhesion layers above and below, deposited by electron-beam

evaporation and etched to form the slots for the antenna and

CPW transmission lines. Since the 620-GHz signal must pass

through the circuit in order to utilize the substrate lens, excess

metal was also etched, leaving only enough in the vicinity of

the transmission lines and antenna to serve as a proper ground

plane. A 1000-

A layer of silicon dioxide was then applied to

provide mechanical and dc isolation between the CPW lines

and subsequent layers. The silicon dioxide was deposited on

the circuit by low-temperature radio frequency (RF) sputtering

using a photoresist lift-off stencil to define small openings

which would allow the thin-film detector and bias wire bonds

to make ohmic contact to the CPW lines beneath it. Two SPB

tuning elements were then added by the process described in

the following section. The final processing layer consisted of

a thermally evaporated 6000-

A-thick bismuth film patterned

with a photoresist lift-off stencil.

IV. SPB T

UNER

ABRICATION

The procedure used for fabricating the micromechanical

SPB tuners on the dielectric-coated CPW lines is illustrated in

Fig. 3. The processing steps are not so different from those for

capacitors and air bridges in fixed tuned circuits, but produce

a more versatile tuning element. Thus, it was possible for

this entire circuit to be fabricated with low-hazard processes

common to high-frequency circuit fabrication without the use

of an environmentally controlled clean room [19], [20].

LUBECKE

et al

.: MICROFABRICATION OF LINEAR TRANSLATOR TUNING ELEMENTS

407

Fig. 3. Simplified illustration of the SPB fabrication process. Sacrificial

layers are used to form an SPB which is constrained by polyimide guide

structures.

A photoresist lift-off stencil was applied and patterned

to define a sacrificial-seed layer. This pattern consisted of

rectangular strips over each CPW line, each as wide as the

SPB (200

m) and extending to the edge of the substrate to

allow for electrode connection. This third layer was formed

by depositing a 1700-

A layer of copper over a 70-

A chrome

adhesion layer through electron-beam evaporation and then

lifting the stencil and unwanted film in acetone.

Next, an 8-

m layer of photoresist was applied to the circuit,

patterned to form a mold layer, and hard baked. This layer

defined the shape of each SPB, several sacrificial pieces used

to define the region into which each SPB would slide, and two

one-square-mm patches. These patterns were all formed over

the sacrificial-seed layer to allow for electroplating, with the

large square patches serving to increase the plating area and

allow for the use of an easily maintained dc plating current.

The wafer was then dipped in gold electroplating solution

where 5-

m-thick patterned gold structures were plated within

the mold, forming the fourth circuit layer.

The mold layer was then striped in N-methyl 2-pyrrolidone,

and a 1-

m sacrificial copper coating was applied to the

exposed SPB and sacrificial structures by connecting the cir-

cuit to an electrode and immersing it in copper electroplating

solution. This formed the fifth circuit layer. A 13-

m-thick

layer of photosensitive polyimide precursor was then spun onto

the circuit and UV patterned to form two digitated strips, each

overlapping a side of the copper-coated gold structures. The

Fig. 4. Microscope photograph showing the removal of two of the sacrificial

gold structures (angled bars) used to form the polyimide guides. Once these

have all been removed, the SPB tuners can slide freely along the transmission

line within the confines of the guides.

strips were then cured in an inert gas environment to form

m-thick polyimide guide structures.

Finally, the copper plating and sacrificial-seed layers were

removed through wet etching to release the gold SPB and

sacrificial structures. The sacrificial pieces shown in Fig. 4

were then removed from under the polyimide guides to allow

the SPB structures to slide within the guides along the surface

of the CPW lines. The digitated structure of the guides both

minimized the chance of binding between the SPB and its

guide and provided reference marks for positioning the tuners.

Fig. 5(a) and (b) shows a scanning electron microscope (SEM)

photograph of a guide structure with its confined SPB in

view and one of a guide structure with its SPB removed,

respectively. Fig. 6 shows a released SPB tuner in its entirety.

The fabrication of state-of-the-art submillimeter-wave inte-

grated circuits typically requires constant painstaking attention,

which is justified by the fact that a single functioning circuit

can yield a great deal of valuable data. The circuit demon-

strated here required a full wafer and seven processing layers

and was no exception. Fabrication, however, was successfully

carried out with very limited processing equipment and in

facilities with little or no environmental regulation. While yield

was not optimized or specifically evaluated, a developmental

wafer processed with an array of ten test tuners yielded six

elements, which could slide smoothly without sticking, and

four damaged elements. Similarly, of the final six circuit

wafers simultaneously processed to produce one suitable for

408

JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 7, NO. 4, DECEMBER 1998

(a)

(b)

Fig. 5. Close-up SEM photograph of one side of an SPB tuner. (a) A polyimide guide structure is shown with a 5-



m-thick SPB beneath it and (b)

another with the SPB removed.

submillimeter-wave measurements, two exhibited tuner bind-

ing—one due to nonuniform gold plating and the other due

to incomplete coverage of the electroplated sacrificial copper.

The yield for producing a functioning submillimeter-wave

bismuth detector in such a circuit is typically lower than that

of these tuners.

V. T

UNER

UNCTION

The processed wafer was mounted over a substrate lens to

allow quasi-optical coupling to a 620-GHz backward wave os-

cillator source. The performance of the integrated SPB tuners

was demonstrated by using them to vary the power delivered

from the slot antenna to the bismuth detector by altering the

impedance match between them. The delivered power was

measured using a lock-in amplifier, and a theoretical model

was also derived to calculate the circuit behavior in order to

predict and verify the measured performance [20].

The tuners were positioned manually using a probe with

an ox-hair tip which provided adequate manipulation control

for the 620-GHz experiment. Ox hair was determined to be

well suited for the application as it had sufficient stiffness for

pushing the tuner, yet could safely brush against the poly-

imide and silicon dioxide surfaces without causing damage.

Power measurements were made for various alignments of

the tuners at 20-

m increments, which is one sixteenth of a

guided wavelength. The circuit was designed to accommodate

movement of the tuners over three guided wavelengths, though

in a practical circuit there would be no need for positioning

LUBECKE

et al

.: MICROFABRICATION OF LINEAR TRANSLATOR TUNING ELEMENTS

409

Fig. 6. SEM photograph of an integrated SPB tuner. An ox-hair probe was used to push each 200-



m-wide SPB along its guide to vary the electrical

length of the CPW line beneath it.

the tuner beyond the first one-half guided wavelength as

the performance pattern repeats after this, only with greater

loss due to the added length of the transmission line. While

over most of the range the tuners exhibited no sticking,

positioning by successive 20-

m increments was difficult and

so the measurements were made for a more or less random

order of tuner positions. The polyimide guides and stopping

structures kept the tuners within the desired range at all times,

and optimum circuit performance could be repeated without

much difficulty. The submillimeter-wave circuit response was

successfully varied over a 15-dB range, which demonstrated

adequate tuning capability for providing a good impedance

match between a wide range of typical submillimeter-wave

devices with high-parasitic reactances, such as SIS devices and

Schottky diodes, and resonant planar antennas, including slots,

dipoles, and self-complimentary structures. Measured results

for independent position sweeps for each SPB tuner agreed

very closely with theory and could be accurately repeated in

tests conducted over a two-week period. The submillimeter-

wave function and performance of this circuit is described in

more detail elsewhere [21], [22].

The fabrication techniques used for the tuner and all-planar

circuitry are well suited to scaling the design to frequencies

up to several terahertz. More precise positioning control may

be necessary in such circuits and could be achieved through

the use of mechanical manipulators such as those used for

positioning optical fibers or through electrostatic [23], shape-

memory alloy [24], or other integrated actuator techniques.

The sliding structure also has the potential to be used for other

micromechanical millimeter- and submillimeter-wave circuit

components such as switches, adjustable antenna elements,

and aperture shutters.

VI. C

ONCLUSION

A new submillimeter-wave tuning element has been devel-

oped along with a technique for its fabrication as an integral

part of a monolithic circuit. The technique is based on silicon

surface micromachining and LIGA, but incorporates only

processes and materials suitable for common submillimeter-

wave integrated circuits. The performance of these tuning

elements has been demonstrated at 620 GHz through me-

chanical manipulation. This is the first reported demonstration

of micromechanically adjustable tuning in a submillimeter-

wave integrated circuit. Potentially, the sliding element can

be adapted to serve additional millimeter- and submillimeter-

wave circuit functions at frequencies up to several terahertz

and, if necessary, could be made to self-actuate through

the application of electrostatic, shape-memory alloy, or other

microelectromechanical actuation techniques, with appropriate

consideration made for individual circuit compatibility with

thermal, electrostatic, and other environmental factors.

CKNOWLEDGMENT

The authors would like to thank P. A. Stimson for his

generous assistance with the submillimeter-wave aspects of

this experiment, E. Kolawa and J. S. Reid for assistance with

dielectric sputtering, and O. Bori

c-Lubecke for assistance with

the manuscript.

EFERENCES

[1] W. Y. Ali-Ahmad, G. M. Rebeiz, H. Dav ́

e, and G. Chin, “802 GHz

integrated horn antennas imaging array,”

Int. J. Infrared and Millimeter

Waves

, vol. 12, no. 5, pp. 481–486, May 1991.

[2] W. R. McGrath, C. K. Walker, M. Yap, and Y.-C. Tai, “Silicon

micromachined waveguides for millimeter-wave and subillimeter-wave

frequencies,”

IEEE Microwave Guided Wave Lett.

, vol. 3, pp. 61–63,

Mar. 1993.

[3] T. M. Weller, L. P. B. Katehi, and G. M. Rebeiz, “A 250 GHz

microshield bandpass filter,”

IEEE Microwave Guided Wave Lett.

, vol.

5, pp. 153–155, May 1995.

[4] L.-S. Fan, Y.-C. Tai, and R. S. Muller, “Integrated moveable microme-

chanical structures for sensors and actuators,”

IEEE Trans. Electron

Devices

, vol. 35, no. 6, pp. 724–730, 1988.

[5] A. B. Frazier and M. G. Allen, “Metallic microstructures fabricated

using photosensitive polyimide electroplating molds,”

IEEE J. Micro-

electromech. Syst.

, vol. 2, no. 2, pp. 87–94, 1993.

[6] I. Mehdi and P. H. Siegel, “Effect of parasitic capacitance on the

performance of planar subharmonically pumped Schottky diode mixers,”

410

JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 7, NO. 4, DECEMBER 1998

5th Int. Symp. Space Terahertz Technology—Symp. Proc.

, May 1994,

pp. 379–393.

[7] R. Blundell and C.-Y. E. Tong, “Submillimeter receivers for radio

astronomy,”

Proc. IEEE

, vol. 80, no. 11, pp. 1702–1720, 1992.

[8] M. Salez, P. Febvre, W. R. McGrath, B. Bumble, and H. G. Leduc,

“An SIS waveguide heterodyne receiver for 600 GHz–635 GHz,”

Int. J.

Infrared and Millimeter Waves

, vol. 15, no. 2, pp. 349–368, Feb. 1994.

[9] J. Zmuidzinas, H. G. Leduc, J. A. Stern, and S. R. Cypher, “Two junction

tuning circuits for submillimeter SIS mixers,”

IEEE Trans. Microwave

Theory Tech.

, vol. 42, no. 4, pp. 698–706, 1994.

[10] R. E. Collin,

Foundations for Microwave Engineering

New York:

McGraw-Hill, 1966.

[11] V. M. Lubecke, W. R. McGrath, and D. B. Rutledge, “Sliding backshorts

for planar circuits,”

Int. J. Infrared and Millimeter Waves

, vol. 12, no.

12, pp. 1387–1397, Dec. 1991.

[12]

, “A 100 GHz coplanar strip circuit tuned with a sliding planar

backshort,”

IEEE Microwave Guided Wave Lett.

, vol. 3, pp. 441–443,

Dec. 1993.

[13] K. C. Gupta, R. Garg, and I. J. Bahl,

Microstrip Lines and Slotlines

Dedham, MA: Artech, 1979.

[14] V. M. Lubecke, W. R. McGrath, and D. B. Rutledge, “Millimeter wave

performance of a sliding planar backshort,” in

SPIE Int. Conf. Millimeter

and Submillimeter Waves and Applications

, Jan. 1994, pp. 543–544.

[15] P. H. Siegel and R. J. Dengler, “The dielectric-filled parabola: A new

millimeter and submillimeter wavelength receiver/transmitter front end,”

IEEE Trans. Antennas Propagat.

, vol. 39, no. 1, pp. 40–47, 1991.

[16] D. P. Neikirk and D. B. Rutledge, “Self-heated thermocouples for far-

infrared detection,”

Appl. Phys. Lett.

, vol. 41, no. 5, pp. 400–402, Sept.

1992.

[17] I. Mehdi, T. H. Lee, D. A. Humphery, S. C. Martin, R. J. Dengler, J.

E. Oswald, A. Pease, R. P. Smith, and P. H. Siegel, “600 GHZ planar-

Schottky-diode subharmonic waveguide mixers,” in

1996 IEEE MTT-S

Int. Symp.

, June 1996, pp. 377–380.

[18] P. A. Stimson

et al.

, “A planar quasioptical SIS receiver,”

IEEE Trans.

Microwave Theory Tech.

, vol. 14, no. 4, pp. 609–615, 1993.

[19] V. M. Lubecke, W. R. McGrath, and D. B. Rutledge, “Micromechan-

ical sliding planar backshorts,” in

Int. Semiconductor Device Research

Symp.

, Charlottesville, VA, Dec. 7, 1995, pp. 477–480.

[20] V. M. Lubecke, “Micromechanical tuning elements for submillimeter

wave integrated circuits,” Ph.D. dissertation, Calif. Instit. Technol.,

Pasadena, CA, July 1995.

[21] V. M. Lubecke, W. R. McGrath, P. A. Stimson, and D. B. Rutledge,

“Micromechanical tuning elements in a 620 GHz integrated circuit,”

IEEE Trans. Microwave Theory Tech.

, to be published.

[22]

, “Performance of micromechanical tuning elements in a 620

GHz monolithic integrated circuit,” in

7th Int. Symp. Space Terahertz

Technology

, Charlottesville, VA, Mar. 1996, pp. 220–233.

[23] T. Akiyama and K. Shono, “Controlled stepwise motion in polysilicon

microstructures,”

IEEE J. Microelectromech. Syst.

, vol. 2, no. 3, pp.

106–110, 1993.

[24] P. Krulevitch, A. P. Lee, P. B. Ramsey, J. C. Trevino, J. Hamilton, and

M. A. Northrup, “Thin film shape memory alloy microactuators,”

IEEE

J. Microelectromech. Syst.

, vol. 5, no. 4, pp. 270–282, 1996.

Victor M. Lubecke

(SM’98) received the B.S. de-

gree in electrical and electronic engineering from the

California State Polytechnical University, Pomona,

in 1986 and the M.S. and Ph.D. degrees in elec-

trical engineering from the California Institute of

Technology, Pasadena, in 1990 and 1995, respec-

tively.

His graduate work focused on high-frequency

integrated-circuit techniques and microelectrome-

chanical systems (MEMS) technology. From 1987

to 1996, he was with the NASA Jet Propulsion

Laboratory working on millimeter- and submillimeter-wave technology in

space communications and remote-sensing applications. Since 1996, he has

been a Visiting Researcher at the Photodynamics Research Center, Institute

for Physical and Chemical Research (RIKEN), Sendai, Japan. His current

research interests include high-frequency integrated circuits, quasi-optics, and

related MEMS techniques.

William R. McGrath

(M’88) received the B.S. degree in physics from the

Massachusetts Institute of Technology, Cambridge, in 1978 and the M.A. and

Ph.D. degrees in physics from the University of California, Berkeley, in 1981

and 1985, respectively.

His graduate work focused on the device physics of SIS mixers and

superconductive circuits. He and his coworkers were the first to measure the

quantum effects of large-gain and quantum-limited noise in SIS mixers at 36

GHz. Upon graduating from the University of California, Berkeley, he took a

position as a Visiting Researcher at the Chalmers University of Technology,

Goteborg, Sweden, where he worked on submillimeter-wave superconductive

detectors. He and coworkers built the first millimeter-wave Josephson effect

mixer using the newly discovered high-Tc superconductors. He joined the staff

of the Jet Propulsion Laboratory, California Institute of Technology, Pasadena,

CA, in 1987, where he became a Group Leader in 1990 and a Technical

Group Supervisor in 1992. He heads a research group which develops high-

performance submillimeter-wave sensors for remote-sensing applications. He

has over 120 publications and two patents.

Dr. McGrath has received several awards related to his research activities.

Yu-Chong Tai

received the B.S. degree in electrical engineering from the

National Taiwan University, Taipei, Taiwan, R.O.C., in 1981 and the M.S.

and Ph.D. degrees from the University of California, Berkeley, in 1986 and

1989, respectively.

He is currently an Associate Professor of Electrical Engineering, California

Institute of Technology, Pasadena, where he directs the Caltech Microma-

chining Laboratory which currently sponsors more than 20 researchers for

micromachining. He has over 12 years of experience doing micromachines

and/or MEMS research. His research interests include MEMS technology,

microsensors, microactuators, microstructures, MEMS systems, and MEMS

science. He has successfully developed MEMS devices in his lab includ-

ing pressure sensors, shear-stress sensors, hot-wire anemometers, magnetic

actuators, microphones, microvalves, micromotors, etc. System-level MEMS

research projects then include integrated M3 (microelectronics

+

microsensors

+

microactuators) drag-reduction smart surface, flexible smart skin for the

control unmanned aerial vehicles, and microfluid delivery systems. He is

also interested in MEMS sciences such as MEMS material (mechanical and

thermal) properties, microfluid mechanics, and micro/nano processing issues.

David B. Rutledge

(M’75–SM’89–F’93) received the B.A. degree in math-

ematics from the Williams College, Williamstown, MA, in 1973, the M.A.

degree in electrical sciences from Cambridge University, Cambridge, U.K.,

in 1975, and the Ph.D. degree from the University of California, Berkeley,

in 1980.

He has been teaching at the California Institute of Technology, Pasadena,

and working on microwave circuits and antennas since 1980. His research

group developed key ideas in integrated-circuit antennas, including lens-

coupled antennas, which appear widely in radio-astronomy receivers. His

group demonstrated anisotropic etching for fabricating horns and mem-

brane technology for suspending metal antennas. The group first described

leakage from planar transmission lines and first demonstrated many active

quasi-optical components, including phase shifters, oscillators, mixers, and

amplifiers. Recently, the group has developed Class-E HF power amplifiers

for industrial and amateur use. He has authored or coauthored over 200

publications. He is a coauthor along with S. Wedge and R. Compton of

the widely distributed educational microwave computer-aided design package

Puff, with 15 000 copies worldwide. He was a Visiting Scientist at CSIRO,

New South Wales, Australia, in the summer of 1985, the Research Institute for

Electrical Communication, Tohoku University, Sendai, Japan, in the Spring

and Summer of 1988, and the National Defense Academy, Yokosuka, Japan,

in the Fall of 1995. He has been a Distinguished Lecturer for the Antennas

and Propagation Society from 1991 to 1993. He has served as Chairman for

19 doctoral candidates.

Dr. Rutledge is a Member of the AP-S AdCom. He received the Teaching

Award of the Associated Students of Caltech. In 1993, he received the MTT-S

Microwave Prize.