Precision Bonding Makes Tiny High Performance Actuators Possible

The new actuators promise to be low cost, and capableof providing controlled force, high resolution and large displacementsappropriate for applications in RF switches for cell phones, forexample, or optical switches for wide screen TVs. Other potentialapplications include microfluidic pumps and valves, micromanipulatorsfor nanoscale handling and atomic force microscope drives.

Dr.Srinivas A. Tadigadapa, associate professor of electrical engineeringand a developer of the bonding process and microactuator, says, "Thesenew piezoelectric microactuators are the first realized usingmicrofabrication methods, a mature technology used to make computerchips and micromachines from silicon-based materials. Our new lowtemperature wafer bonding techniques, which make the actuatorspossible, can also be used for precision integration of dissimilarmaterials in other micro-electro-mechanical systems."

The newactuators and bonding process are described in a paper, Fabrication andperformance of a flextensional microactuator, which appears in thecurrent online edition of the Journal of Micromechanics andMicroengineering (JMM). The paper will also be featured in the Octoberprint version of JMM.

The authors are Jongpil Cheong, who earnedhis doctorate at Penn State this year, Abhijat Goyal, a doctoralcandidate in electrical engineering, Dr. Tadigadapa and Dr. ChristopherD. Rahn, professor of mechanical engineering.

The new actuatorsare made from flat strips of bulk PZT, a commercially availablepiezoelectric material that shrinks slightly when a voltage is appliedto it, and a precision micromachined silicon beam. Bonding the siliconbeam to the PZT amplifies and converts the PZT shape change into aconvex deflection when the silicon beam buckles as the PZT shrinks.

Inoperation in the actuator, the measured deflection of the silicon beamshows a gain factor of 20 with respect to the PZT dimensional change.

Forthe bonding process in fabricating the new actuators, the Penn Stateresearchers use photolithography and low temperature solders to producethe distinctive bridge shape they need.

Dr. Tadigadapa notes,"The PZT depoles if you heat it too high. Therefore, the temperature iscrucial. A low temperature solder bonding process at 200 C was used inthis work."

Using their new approach, the researchers havefabricated actuators with dimensions ranging from 350 to 600 microns inlength, 50 to 100 microns (about the width of a human hair) in width,and 5 to 6 microns in thickness.

In tests, the actuators showedgood repeatability with a large amplitude stroke of about 8 micronswhen actuated using -100V to 100V. The bandwidth of the actuator wasmeasured at 265 KHz.