Coils, filters, switches and capacitors manufactured with micromechanics for RF

RF MEMS

Ericsson Hopes for
Mechanical Mobiles

Coils, filters, switches and capacitors manufactured  with micromechanics for RF sector provide more

compact and energy-efficient designs.

When mechanics in micro-format can replace traditional

electronics, mobile phones can be made both smaller

and more energy-efficient. These are the expectations

of both researchers and industry when it comes to the

future of micromechanics in the RF (radio frequency) sector.

JONAS RYBERG

MEMS, or micro-electro-mechanical systems, have

now found applications as blood pressure meters in the

medical industry, mirrors in projectors and as a

ccelerometers in the automotive industry. But small

mechanical structures can also be used as building

blocks in a radio. In research labs around the world,

there are now MEMS components that can replace

electronic switches, radio filters, coils and capacitors

in transmitters and receivers. But the big break-through,

as well as the introduction of commercial products,

will have to wait for the time being.

"It's not just a matter of developing a component; it must

also be mass-produced," says Shu-Ang Zhou, who

coordinates Ericsson's RF MEMS efforts.

He and Ericsson are not interested in just a few

components; for RF MEMS to be of interest, it must

be possible to develop components with good

performance at competitive prices and in runs that

suffice for mass-produced mobile phones. Ericsson

is now looking both at RF switches for smart antennas

and filters, coils and capacitors in MEMS structures.

"I believe that MEMS will initially be in the terminals

because the technology makes it possible to reduce

both energy consumption and size. In base stations,

energy consumption and size are not as important."

The reason for Shu-Ang Zhou, as well as many others,

putting so much hope in RF MEMS is that constructions

can be made for which energy loss is insignificant in

comparison with today's electronics solutions.

An example is a diode or transistor switch that is

replaced by a mechanical switch in an antenna.

While the diode constantly consumes power, the

mechanical switch functions like a common relay.

Moreover, MEMS components have good linearity

and high bandwidth, which is important for future

broadband radio communications systems.

SLOWER THAN ELECTRONICS

The disadvantage is that mechanics are slower than

electronics, but for switching antenna elements in a

smart antenna, mechanics are fast enough.

It is not just the power benefits that make Shu-Ang Zhou

believe that the telephone will be the first application for

RF MEMS.

"There is also the uncertainty of how reliable the

components are that will result in them being used in

the terminals first. One might have a terminal for two

or three years; a base station should last considerably

longer."

Edvard Kälvesten, president of the Swedish MEMS

company Silex, believes, however, that the base station

can become the first application for which RF MEMS

comes into use.

"It will be difficult, price-wise, to replace existing

components in mobile telephones. However in the

base station, it's acceptable if it costs more."

His company is conducting a project with RF MEMS

together with an unnamed customer. They expect, just

as Ericsson, that products will be introduced within

three years. "Of our products, RF MEMS is the one

that demands the longest take-off run," Kälvesten explains.

According to Shu-Ang Zhou, Ericsson does not plan

to manufacture its own RF MEMS components. Instead,

collaboration is underway with likely subcontractors,

for example, Philips Semiconductors. This is the procedure

the company employs with most of its components, but in

the MEMS area, collaboration can demand more.

"It's a little different because it's an entire system. This

requires that the system engineer works together with the

component manufacturer."

EUROPEAN PROJECT

Collaboration with Philips is conducted, in among other

ways, through the newly started EU project Mems2Tune,

which shall run for a period of three years and target the

development of switches and adjustable capacitors.

Joost van Beek from Philips is leading the project, and

precisely as his Ericsson colleagues, is convinced that the

future is in mass-produced MEMS for mobile telephones.

"Philips is most interested in the applications for

mass-produced electronics, and the market for RF MEMS

is there if you can just make a sufficiently inexpensive and

reliable product. I don't believe that that a switch in

RF MEMS needs to be more expensive than a

corresponding diode switch."

For Philips, the focus is on development in producing

MEMS products that can be manufactured in a process

that is as close as possible to the standard processes that

they already use.

"We feel that only small modifications are needed to be

able to use MEMS and we are exerting ourselves to change

as little as possible," says Joost van Beek.

    Aside from the adaptation of production for RF MEMS,

the major challenge facing Philips and the other manufacturers

is in finding packaging that is sufficiently inexpensive and

substantial to protect the mechanical parts.

"At present, there is no satisfactory standard packaging

for MEMS," says Joost van Beek.

On the Mems2Tune project, it is the research institute

Umec that is working with packaging. But Philips also has

a project underway on which attempts are being made to

construct packing directly on the silicon chip at the same

time as the MEMS circuit is manufactured.

BELIEF IN PRODUCTION THIS YEAR

The problem with the small switches is that dampness

and oxygen, for example, can cause the switches to

corrode and perhaps fasten in one position. But even

for other structures such as resonators, the packaging

issue is a problem.

Because of the resonators' smallness, the surrounding

air influences how well they oscillate. For this reason,

efforts are being directed towards including a vacuum

in the packaging.

Joost van Beek believes that there can be products that

employ RF MEMS technology on the market as early

as this year, but not from Philips. Which company that

will be first, he does not wish to reveal, but he believes

that the first products will be switches.

   Another company that has had projects with

RF MEMS is the antenna manufacturer Allgon.

But there, development has been on hold as of late.

"The market is more focused on the immediate future

and is today less inclined to take risks when we've had

a year without growth behind us. Functioning MEMS

at a reasonable price is further away and we are less

active just now when it comes to RF MEMS," says

Björn Berndtsson of Allgon Mobile Communications.

Motorola, which previously conducted MEMS

projects with Allgon, has developed a switch that is

now undergoing durability testing in their labs.

"We've demonstrated switches that manage ten billio

n switchings without failure," says Regina Cirmonova,

press spokeswoman at MotorolaSemiconductors'

product department in Geneva.

For the future, the dream among researchers is to be

able integrate MEMS and electronics on the same plate.

"It's hard to get it to work; each part of the production

chain weakens it," says Peter Enoksson, a professor in

microsystems at the Chalmers University of Technology

in Gothenburg, Sweden.

"The components today are often a combination, perhap

s in the same package. But we are looking at which ways

are best for integrating them, for example, as flip chips or

multi-chip models."

Página: www. radantmems.com

Realizado: Franco A Rivera C.

Asignatura: CRF