Aluminum nitride on titanium for CMOS compatible piezoelectric transducers

Abstract

Piezoelectric materials are widely used for microscale sensors and actuators but can pose material compatibility challenges. This paper reports a post-CMOS compatible fabrication process for piezoelectric sensors and actuators on silicon using only standard CMOS metals. The piezoelectric properties of aluminum nitride (AlN) deposited on titanium (Ti) by reactive sputtering are characterized and microcantilever actuators are demonstrated. The film texture of the polycrystalline Ti and AlN films is improved by removing the native oxide from the silicon substrate in situ and sequentially depositing the films under vacuum to provide a uniform growth surface. The piezoelectric properties for several AlN film thicknesses are measured using laser doppler vibrometry on unpatterned wafers and released cantilever beams. The film structure and properties are shown to vary with thickness, with values of d 33f , d 31 and d 33 of up to 2.9, −1.9 and 6.5 pm V −1 , respectively. These values are comparable with AlN deposited on a Pt metal electrode, but with the benefit of a fabrication process that uses only standard CMOS metals.

New Devices for Investigating Hair Cell Mechanical Properties

“…The force probe is manufactured on a silicon wafer using techniques that we have previously reported [2,3]. The probe dimensions are defined lithographically and over a hundred are produced in parallel on each wafer.…”

Preparation of (001) preferentially oriented titanium thin films by ion-beam sputtering deposition on thermal silicon dioxide

“…Titanium thin films have been used as sensing electrodes, buffer, or adhesive layers. The advantages of titanium thin films are good electric conductivity, extraordinary chemical resistivity, thermal stability, high hardness, high melting point, and lower number of crystallographic imperfections [1][2][3][4][5]. Crystallographic orientation of titanium thin films has to be controlled during the deposition process to obtain specific properties (e.g., mechanical, chemical) suitable for an eventually required application [6,7].…”

The extraordinary role of the AlN interlayer in growth of AlN sputtered on Ti electrodes

“…Recently, Ti electrodes have been investigated as an alternative for CMOS compatibility. 9 However, a lower quality of the AlN layers has been reported in comparison to AlN deposited on Pt. 9,10 By using an AlN interlayer below the Ti an improved crystallinity and orientation of the AlN layers has been observed.…”

“…9 However, a lower quality of the AlN layers has been reported in comparison to AlN deposited on Pt. 9,10 By using an AlN interlayer below the Ti an improved crystallinity and orientation of the AlN layers has been observed. 9,10 This is attributed to the decrease of the crystallization energy of the electrodes possibly caused by the AlN interlayer.…”

“…9,10 By using an AlN interlayer below the Ti an improved crystallinity and orientation of the AlN layers has been observed. 9,10 This is attributed to the decrease of the crystallization energy of the electrodes possibly caused by the AlN interlayer. 10,11 Recently, we reported on the use of this interlayer as a stop layer when releasing MEMS piezoelectric actuators.…”