Highly piezoelectric co-doped AlN thin films for wideband FBAR applications

Abstract

We report piezoelectric materials composed of charge-compensated co-doped (Mg, β)(x)Al(1-x)N (β = Zr or Hf) thin films. The effect of the dopant element into AlN on the crystal structure, and piezoelectric properties of co-doped AlN was determined on the basis of a first-principles calculation, and the theoretical piezoelectric properties were confirmed by experimentally depositing thin films of magnesium (Mg) and zirconium (Zr) co-doped AlN (Mg-Zr-doped AlN). The Mg-Zrdoped AlN thin films were prepared on Si (100) substrates by using a triple-radio-frequency magnetron reactive co-sputtering system. The crystal structures and piezoelectric coefficients (d33) were investigated as a function of the concentrations, which were measured by X-ray diffraction and a piezometer. The results show that the d33 of Mg-Zr-doped AlN at total Mg and Zr concentrations (both expressed as β) of 0.35 was 280% larger than that of pure AlN. The experimentally measured parameter of the crystal structure and d33 of Mg-Zr-doped AlN (plotted as functions of total Mg and Zr concentrations) were in very close agreement with the corresponding values obtained by the first-principle calculations. Thin film bulk acoustic wave resonators (FBAR) employing (Mg,Zr)0.13Al0.87N and (Mg, Hf)0.13 Al0.87N as a piezoelectric thin film were fabricated, and their resonant characteristics were evaluated. The measured electromechanical coupling coefficient increased from 7.1% for pure AlN to 8.5% for Mg-Zr-doped AlN and 10.0% for Mg- Hf-doped AlN. These results indicate that co-doped (Mg, β)(x)Al(1-x)N (β = Zr or Hf) films have potential as piezoelectric thin films for wideband RF applications.

Giant Reflection Coefficient on Sc0.26Al0.74N Polycrystalline Diamond Surface Acoustic Wave Resonators

“…[11] Several authors have modeled thin-film bulk acoustic resonator (FBAR) on AlN and ScAlN thin films. [28,29] However, a proper comparison with those values cannot be performed for different device technologies.…”

“…Although this metal is more resistive than other metals usually used in microfabrication technologies such as Au or Cu, it is extensively used for high‐temperature applications due its high thermal stability . Several authors have modeled thin‐film bulk acoustic resonator (FBAR) on AlN and ScAlN thin films . However, a proper comparison with those values cannot be performed for different device technologies.…”

Materials, Design, and Characteristics of Bulk Acoustic Wave Resonator: A Review

“…The elements include Sc [ 26 , 27 , 45 , 46 , 47 , 48 , 49 ], Ti [ 50 , 51 ], Ta [ 25 , 52 ], V [ 52 ], Y [ 53 ], Mg [ 54 ], and Er [ 55 ]. The co-doping element includes Mg+Zr [ 56 , 57 ], Mg+Hf [ 57 , 58 ], Mg+Nb [ 59 , 60 ], and Mg+Ti [ 61 ]. Sc, Ta, Y, and Er increase the piezoelectric properties of the film within a certain doping concentration range.…”

Piezoelectricity, Phase Stability, and Surface Diffusion in Multicomponent Nitrides

“…So far there have been little experimental work on these quarternary alloys, limited to that of Yokoyama et al [80,81] and Minh et al [82,83], who have synthesized TM x/2 Mg x/2 Al 1−x N alloys and create devices with x ≤ 0.348.…”