Marc-Alexandre Dubois

Properties of aluminum nitride thin films for piezoelectric transducers and microwave filter applications

Aluminum nitride thin films have been grown by reactive magnetron sputter technique using a pulsed power supply. The highly (002)-textured columnar films deposited on platinized silicon substrates exhibited quasi-single-crystal piezoelectric properties. The effective d33 was measured as 3.4 pm/V, the effective e31 as 1.0 C/m2. The pyroelectric coefficient turned out to be positive (4.8 μCu200am−2u200aK−1) due to a dominating piezoelectric contribution. Thin-film bulk acoustic resonators (TFBAR) with fundamental resonance at 3.6 GHz have been fabricated to assess resonator properties. The material parameters derived from the thickness resonance were a coupling factor k=0.23 and a sound velocity vs=11u200a400u200am/s. With a quality factor Q of 300, the TFBARs proved to be apt for filter applications. The temperature coefficient of the frequency could be tuned to practically 0 ppm/K.

Stress and piezoelectric properties of aluminum nitride thin films deposited onto metal electrodes by pulsed direct current reactive sputtering

Polycrystalline aluminum nitride thin films were deposited onto platinum, aluminum, and titanium electrodes by reactive magnetron sputtering in the pulsed direct current mode. The films exhibited all a columnar microstructure and a c-axis texture. The built-in stress and the piezoelectric properties of these films were studied as a function of both the processing conditions and the electrode material. Stress was found to be very much dependent on the growth conditions, and values ranging from strong compression to high tension were observed. The piezoelectric d33,f coefficient was shown to rely on substrate quality and ionic bombardment: The nucleation surface must be stable with regard to the nitrogen plasma and present a hexagonal symmetry and, on the other hand, enough energy must be delivered to the growing film through ionic bombardment.

Measurement of the effective transverse piezoelectric coefficient e31,f of AlN and Pb(Zrx,Ti1−x)O3 thin films

The effective piezoelectric transverse coefficient e(31,f) was measured on various lead zirconate-titanate (PZT) and aluminum nitride thin films. The measurement set-up is based on the collection of the electric charges created by the forced deflection of a Si cantilever coated with a piezoelectric material. The maximum value was obtained from a tetragonal composition of PZT (45/55 Zr/Ti ratio) and was equal to 8.3 C/m(2). The ALN layer exhibited 97% of the theoretical value calculated from single crystal data, i.e., e(31,f)- = 1.02 C/m(2) (C) 1999 Elsevier Science S.A. All rights reserved.

Integration of high-Q BAW resonators and filters above IC

A double-lattice BAW filter with balanced input and output is designed with a center frequency of 2.14GHz. The filter is integrated directly above a 0.25/spl mu/m BiCMOS RF IC. Insertion loss of -3dB and out-of-band rejection better than -50dB are achieved. An integrated LNA comprising two broadband amplifiers and one BAW filter is also presented.

Which PZT thin films for piezoelectric microactuator applications

Abstract The effective piezoelectric coefficient e31 has been measured on sol-gel processed Pb(ZrxTi1−x)O3 thin films with Zr concentrations ranging from 45 to 60%. The largest value was observed at 45% Zr, although dielectric constant and effective d33 peak at 53% Zr. The findings suggest that the optimal composition for microactuators and sensors is less than 45% Zr, i.e., in the tetragonal part of the phase diagram.

Solidly mounted resonator based on aluminum nitride thin film

A piezoelectric thin film sandwiched between two conductors is the basic structure for high frequency bulk acoustic wave devices. For that purpose, AlN thin films deposited by DC reactive sputtering on various electrode materials were investigated. Highly c-axis oriented thin films as thick as 2 /spl mu/m were grown and analyzed. Intrinsic stress values ranging from strong compression to high tension were observed and piezoelectric d/sub 33,f/ coefficients up to 3.9 pm/V were measured. Solidly mounted resonators with a 10-layer acoustic reflector have been fabricated. They exhibited a pronounced resonance peak centered at 2 GHz with a high Q factor and a k/sup 2/ coupling coefficient of 1%. These characteristics are discussed as a function of the processing conditions and the thin film properties.

ALUMINUM NITRIDE THIN FILMS FOR HIGH FREQUENCY APPLICATIONS

Abstract A piezoelectric thin film sandwiched between two conductors is the basic structure for high frequency bulk acoustic wave devices. For that purpose, AIN thin films deposited by DC reactive sputtering on various electrode materials were investigated. Highly c-axis oriented thin films as thick as 2.5 μm were grown on various substrates and analyzed. Intrinsic stress values ranging from strong compression to high tension were observed and piezoelectric d33, f coefficients up to 3.9 pm/V were measured. The first fabricated acoustic resonators showed a pronounced resonance peak centered at 2 GHz with a very high Q factor.

Microstructure and defects of wurtzite structure thin films

ZnO and AlN, which exhibit the wurtzite structure, were deposited onto metal coated SiO2 substrates by sputtering. X-ray diffraction (XRD) indicated that the films contained no second phases and exhibited an [0001] texture. Transmission electron microscopy (TEM) observations confirmed the XRD results and revealed the columnar microstructure of the films. The width of the columnar grains were less than 30 nm for AIN and between 100 and 400 nm for ZnO. In the ZnO grains, a large concentration of defects were identified, which included dislocations and stacking faults that lie on the basal plane

Solidly mounted BAW filters for the 6 to 8 GHz range based on AlN thin films

Bulk acoustic wave (BAW) resonators and filters have been fabricated in the frequency range between 7 and 8 GHz. Resonators with quality factors of 400 to 600, and coupling factors k/sup 2/ of 4 to 5.5% have been achieved. The obtained resonator characteristics theoretically yield filters of 3.5% 3 dB bandwidths with flat channel characteristics, and insertion losses of -6 dB. The trade-offs related to the use of aluminum or platinum bottom electrodes is investigated theoretically. While aluminum is expected to yield filters with lower insertion loss, Pt is expected to yield larger bandwidths.

In-plane piezoelectric coefficient of PZT thin films as a function of composition

The effective piezoelectric coefficient e(31) has been measured on sol-gel processed Pb(ZrxTi1-x)O-3 thin films with Zr concentrations ranging from 45 to 60%. The largest value was observed at 45% Zr, although dielectric constant and effective d(33) peak at 53% Zr. The findings suggest that the optimal composition for microactuators and sensors is less than or equal to 45% Zr, i.e., in the tetragonal part of the phase diagram.