Piezoelectric actuation of microbridges using AlN

Abstract We demonstrate the piezoelectric actuation of a microbridge based on a sputtered aluminium nitride (AlN) thin film. The suspended microbridge consists of a silicon nitride structural layer supporting a Mo/AlN/Mo actuator. A complete technology for the fabrication of the microactuators, fully compatible with standard silicon ICs technologies, has been developed. It includes: (1) the selection of the substrate and the structural layer, (2) the selection of molybdenum as metal for the bottom electrode, (3) the optimization of the sputtering of AlN on molybdenum in order to achieve (002) oriented films with good crystal quality, low residual stress and good piezoelectric response and (4) the fine tuning of the surface micromachining techniques necessary to release the whole structure. Preliminary results on the characteristics of the microactuators are reported. An actuation voltage of 16 V applied to a 350 μm-long bridge produces a deflection of 3.5 μm with negligible current consumption.

[1]  L. Vergara,et al.  A model for the accurate determination of the electromechanical coupling factor of thin film SAW devices on non-insulating substrates , 2004, IEEE Ultrasonics Symposium, 2004.

[2]  G. Stoney.  The Tension of Metallic Films Deposited by Electrolysis , 1909 .

[3]  M. A. Respaldiza,et al.  Influence of oxygen and argon on the crystal quality and piezoelectric response of AlN sputtered thin films , 2004 .

[4]  M. Aguilar,et al.  Influence of sputtering mechanisms on the preferred orientation of aluminum nitride thin films , 2003 .

[5]  S. Trolier-McKinstry,et al.  Piezoelectric films for MEMS applications , 2001, Proceedings. 11th International Symposium on Electrets.

[6]  Y. Morilla,et al.  Comparative study of c-axis AlN films sputtered on metallic surfaces , 2005 .

[7]  N. Rimmer,et al.  Integrated approach to electrode and AIN depositions for bulk acoustic wave (BAW) devices , 2003 .

[8]  K. Kusaka,et al.  Effect of sputtering gas pressure and nitrogen concentration on crystal orientation and residual stress in sputtered AlN films , 2002 .

[9]  E. J. Mittemeijer,et al.  The determination of crystallite-size and lattice-strain parameters in conjunction with the profile-refinement method for the determination of crystal structures , 1983 .

[10]  S. J. Gross,et al.  Lead-zirconate-titanate-based piezoelectric micromachined switch , 2003 .

[11]  Enrique Iborra,et al.  Piezoelectric properties and residual stress of sputtered AlN thin films for MEMS applications , 2004 .

[12]  Jin-Seok Park,et al.  Effects of bottom electrodes on the orientation of AlN films and the frequency responses of resonators in AlN-based FBARs , 2003 .

[13]  I. Katardjiev,et al.  Synthesis of c-axis oriented AlN thin films on metal layers: Al, Mo, Ti, TiN and Ni , 2002, 2002 IEEE Ultrasonics Symposium, 2002. Proceedings..

[14]  Gabriel M. Rebeiz.  RF MEMS: Theory, Design and Technology , 2003 .

[15]  Wolfgang Brand,et al.  Piezoelectric thin AlN films for bulk acoustic wave (BAW) resonators , 2003 .

[16]  M. Aguilar,et al.  Effect of particle bombardment on the orientation and the residual stress of sputtered AlN films for SAW devices , 2004, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[17]  A. Hårsta,et al.  Synthesis of highly oriented piezoelectric AlN films by reactive sputter deposition , 2000 .

[18]  Paul Muralt,et al.  Stress and piezoelectric properties of aluminum nitride thin films deposited onto metal electrodes by pulsed direct current reactive sputtering , 2001 .