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

Abstract

In this paper, we report new piezoelectric materials composed of charge-compensated co-doped (Mg, ) x Al 1-x N ( = Zr or Hf). The effect of the dopant element into AlN on chemical stability, crystal structure, and piezoelectric property of co-doped AlN was determined on the basis of first-principles calculation, and the theoretical piezoelectric property was 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 a triple-radio-frequency magnetron reactive co-sputtering system. The crystal structures and piezoelectric coefficients (d 33 ) of the films were investigated as a function of their concentrations, which were measured by X-ray diffraction and a piezometer. The investigation results show that d 33 of Mg-Zr-doped AlN at total Mg and Zr concentrations (both expressed as x) of 0.35 is 280% larger than that of pure AlN. The experimentally measured parameter of the crystal structure and d 33 of Mg-Zr-doped AlN (plotted as functions of total Mg and Zr concentrations) are in very close agreement with the corresponding values obtained by first-principle calculations. Thin film bulk acoustic wave resonators (FBARs) employing (Mg,Zr) 0.13 Al 0.87 N and (Mg,Hf) 0.13 Al 0.87 N as a piezoelectric thin film were fabricated, and their resonant characteristics were evaluated. As a result, the measured electromechanical coupling coefficient was found to increase 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 codoped (Mg, ) x Al 1-x N ( = Zr or Hf) films have potential as piezoelectric thin films for wideband RF applications.

Large piezoelectric response of quarternary wurtzite nitride alloys and its physical origin from first principles

“…In TM Compared to previously reported piezoelectric coefficients e 33 , C 33 , and d 33,f by Yokoyama et al [11,13] and Iwazaki et al [12] there is a qualitative agreement that the quarternaries will be an improvement compared to pure AlN and a competitive alternative to ScAlN. There are, however, some quantitative differences, which is expected because of the different alloy models used.…”

“…Here, we investigate the piezoelectric and elastic properties of the nine different quarternary TM x/2 M x/2 Al 1−x N (TM = Ti, Zr, Hf; M = Mg, Ca, Zn) alloys. Of these quarternaries, TiMgAlN [11,12], ZrMgAlN [11][12][13][14], and HfMgAlN [11,12] have only recently begun to be studied theoretically, and only ZrMgAlN [11,13] and HfMgAlN [11] experimentally. Moreover, we investigate the thermodynamic stability of the alloys to determine the possibilities for equilibrium or the need for nonequilibrium synthesis routes.…”

Acoustic properties of co-doped AlN thin films at low temperatures studied by picosecond ultrasonics

“…Other doping elements have been, therefore, investigated; Yokoyama et al proposed (Mg 0.5 Zr 0.5 ) x Al 1−x N and (Mg 0.5 Hf 0.5 ) x Al 1−x N and indicated the enhancement in d 33 by a factor approximately 3 at x = 0.13. 10,11) However, their important acoustic properties such as sound velocities, elastic constants, and their temperature coefficients remain unclear.…”

Influence of sputtering atmosphere on crystal quality and electrical properties of zirconium aluminum nitride thin film

“…The crystal structure and orientation of the films were investigated by X-ray peaks, which first decreases and then increases with increasing N 2 /Ar-flow ratios and pressures, and reaches the optimal value of 4.68°, which is superior to those values previously published in [8,12], as shown in Figs. 1 (c) and (d).…”