MEMS Based reconfigurable Patch antenna

8/12/2019 MEMS Based reconfigurable Patch antenna

1/30


2/30

WHAT IS MICRO MACHINED WIDEBAND FREQUENCYRECONFIGURABLE MICROSTRIP PATCH ANTENNA?

IDEA BEHIND RECONFIGURABLE MICROSTRIP PATCH ANTENNAREQUIREMENTS ANTENNA CONFIGURATIONOPERATING PRINCIPAL

MEMS ACTUATOR CONFIGURATION AND DESIGN

FABRICATION PROCESSCONCLUSION

ADVANTAGES

BIBLOGRAPHY


3/30

This is a tunable antenna system which isfabricated by a combination of surface and bulkmicromachining processes.

Thermal actuation is employed to precisely adjustthe operating frequency with voltage rangescompatible with todays CMOS circuitries i.e.,MEMS-based actuation mechanisms.


4/30

Idea behind these smart antennas in high-performance wireless communication systems isthe ability of precisely adjusting the operatingfrequency, while retaining the same radiationpattern within the tuning range.

It improves the flexibility and performance ofcordless communication systems by eliminatingthe need for various antenna systems operating atdifferent frequencies in different applications.


5/30

Thermal actuatorsMeandered springsSilicon membraneGolden antenna patchFeed line


6/30

It consists of two segments; a micro machinedsilicon chip (upper segment) and a 500 -m thickRF-module (lower segment).

Fabrication of upper segment includes thermalactuators, meandered springs and 4-m -thicksuspended silicon membrane.

The hot-arms of the thermal actuators are formedby surface micromachining over the silicon chip, while the suspended silicon membrane,meandered springs and cold-arms are fabricated

by bulk micromachining.


7/30

The dimension of the suspended silicon

membrane ( r=11.9 ) is 4mm 4mm and serves as aplatform for a 3mm 3mm thin golden patch.

The lower segment incorporates the proximity feedsystem.

Mounting the silicon chip over the RF-moduleintroduces an air gap of 114 m between antennapatch and feed line.


8/30


9/30

The dielectric material type and its thickness havea significant effect on resonant frequency of themicrostrip patch antennas.

The dielectric layer is composed of epitaxial silicon(silicon membrane), air gap cavity and RF-module.

The main idea is to introduce an adjustable air gapbetween the antennas patch and ground plane.


10/30


11/30

Controlling the height of the air gap gives the

antenna frequency tuning capability.

Downward deflection of the suspended silicon

membrane by thermal actuators reduces the airgap height and hence changes the effectivedielectric constant of the antenna.

Any variation in the effective dielectric constantinfluences the operating frequency of the antenna.


12/30

Figure indicates, with decreasing the air gap, resonantfrequency of the antenna decreases.


13/30

To investigate the effect of initial air gap height andits variations on the achievable tuning range fewantennas were designed with different initial air gapand different operating frequencies.

Simulation results are summarized in table revealsthat the 23.11 GHz antenna with initial air gap of120 m provides larger frequency shift as a function of

downward deflection of the patch


14/30

For large air gap height, a large actuation voltage isrequired so, electro-thermal actuation is used.

Electro-thermal microactuators have the advantage ofachieving higher deflections by actuation voltageranges compatible with todays CMOS circuitries.

A horizontal U-shape electro-thermal actuatorconsisting two layers separated by an air gap betweenthem is used.


15/30

The upper layer, to which actuation voltage is

applied, called hot arm and is fabricated by surfacemicromachining of a polysilicon layer over theepitaxial silicon.

The lower layer called cold arm and is formed bybulk micromachining of epitaxial layer of silicon.

Both layers are connected on the tip of themicroactuator by a shuttle through a very thinlayer of silicon nitride which serves as an electricalisolator.


16/30


17/30

By applying an actuation voltage, two hot-arms

elongate and deflect the tip of the actuatordownward.

Power dissipation and thermal distribution aremain issues because as deflection produced bythermal actuator increases, the tuning range of theantenna increases too.


18/30

A tuning range of 440 MHz can be achieved by adownward deflection of 3m from 114 m up-state

position.


19/30

A 0.75- m -thick silicon-oxide layer is grown by thermaloxidation and formed as sacrificial layer.

The process begins with a chemical-physicalpolishing of a silicon substrate to a height of 120 m.


20/30

For electrically isolating between hot and cold arms, a200 nm thick layer of silicon-nitride is coated by PECVD

process and structured.


21/30

For formation of hot-arms and shuttle a 2-m thick polysilicon layer is deposited and structured by RIE

process.


22/30

The hot-arms are released by etching the sacrificiallayer in a gas phase HF.


23/30

To formation of the patch, a 150 nm gold layer isdeposited through lift-off process.


24/30

A bulk etching on the back side of the silicon substrate isperformed by KOH solution to form a 4- m -thick silicon

membrane.


25/30

By the aid of a very thick photoresist layer, the RIE isperformed to form the cold arms, meandered springs and

floating silicon membrane.


26/30

Thermal actuators operates at voltage levelscompatible with CMOS circuitries.

A tuning range of 440 MHz was achieved by anactuation voltage of 1.5 V.

This antenna employing MEMS technology is lowpower, low cost and low size that have excellentfunctionality within the tuning range.


27/30

Improved the flexibility and performance byeliminating the need for various antenna systems

operating at different frequencies.

Ability of precisely adjusting the operating frequency, while retaining the same radiation pattern within thetuning range.

Electro-thermal microactuators have the advantage ofachieving higher deflections with considerable forceover electrostatic actuation


28/30

An electro-thermally driven reconfigurable microstrippatch antenna has a stable radiation pattern withinthe tuning range.

The up-state operating frequency of the antenna is22.61 GHz which continuously can be lowered to22.17 GHz.

A tuning range of 440 MHz is achieved by anactuation voltage range of 0-1.5 V.


29/30

J.S. Dahele, Sen. Mem, and K.F. Lee, "Theory and

experiment on microstrip antennas with air gaps" 1EEPROCEEDINGS, Vol. 132, Pt. H, No. 7, December 1985.

Caglar Elbuken, Nezih Topaloglu,,Patricia M. Nieva,,Mustafa Yavuz, Jan P. Huissoon, "Modeling and analysis ofa 2-DOF bidirectional electro-thermal microactuator," Microsyst Technol:713-722, 16 January 2009.

D. Yan, "Mechanical Design and Modeling of MEMSThermal Actuators for RF Applications," Master of AppliedScience, Waterloo, 2002.

Vijay K. Varadan, K. J. V., and K.A. Jose, RF MEMS and their

applications, Wiley, 2002, pp. 1-105,344-364.


30/30

Documents

MEMS Based reconfigurable Patch antenna