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Formation energies of the dopant elements in AlN obtained from ab initio calculations. Calculations are performed with supercells composed of 3 × 3 × 2 AlN unit cells (72 atoms). Numbers in parentheses denote the possible valence states of the dopant elements in the formation energy diagram calculated using Eq. (1). Bold numbers in these parentheses are the valence states of the dopants at EF = Eg/2.
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We propose a series of new compositions of AlN-based piezoelectric material based on the results of first-principles calculation. The composition is expressed by Al1−xN, where the elements α and β are selected to maintain the charge neutrality of the host AlN. We found that the selection of Mg2+ for α and Hf4+ and Zr4+ for β with y = 0.5 show good...
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The current work deals with the review of various piezoelectric materials and their piezoelectric coefficient (d33) for probable piezoelectric device applications. In addition, the comprehensive analysis of the data of d33 obtained for distinct compounds is also made. Furthermore, the best suited material compositions are highlighted.
The current work deals with the review of various piezoelectric materials and their piezoelectric coefficient (d 33) for probable piezoelectric device applications. In addition, the comprehensive analysis of the data of d 33 obtained for distinct compounds is also made. Furthermore, the best suited material compositions are highlighted.
Citations
... Co-alloying double TMs provides more room for regulation. Mg x TM y Al 1-(x+y) N (TM = Ti, Zr, and Hf ) was theoretically investigated, and the larger ionic radii of TM were demonstrated to contribute to the increase of piezoelectric performance [137]. The weaker TM-N bonds in Mg x TM y Al 1-(x+y) N (TM = Ti, Zr, Hf, Nb, Cr, Mo, and W) were determined to be one origin of the elastic soften, and which further increased the d 33 [138,139]. ...
Bandpass filters with high frequency and wide bandwidth are indispensable parts of the fifth-generation telecommunication technologies, and currently, they are mainly based on surface and bulk acoustic wave resonators. Owing to its high mechanical strength, excellent stability at elevated temperatures, good thermal conductivity, and compatibility with complementary metal-oxide-semiconductor technology, aluminum nitride (AlN) becomes the primary piezoelectric material for high-frequency resonators. This review briefly introduces the structures and key performance parameters of the acoustic resonators. The common filter topologies are also discussed. In particular, research progresses in the piezoelectric AlN layer, electrodes, and substrates of the resonators are elaborated. Increasing the electromechanical coupling constant is the main concern for the AlN film. To synthesize AlN in single-crystalline or poly-crystalline with a high intensity of (0002) orientation, and alloy the AlN with other elements are two effective approaches. For the substrates and bottom electrodes, lattice and thermal expansion mismatch, and surface roughness are critical for the synthesis of a high-crystal-quality piezoelectric layer. The electrodes with low electrical resistance, large acoustic-impedance mismatch to the piezoelectric layer, and low density are ideal to reduce insertion loss. Based on the research progress, several possible research directions in the AlN-based filters are suggested at the end of the paper.
... Various material descriptors, especiallly the lattice c a ratio, have been identified as key properties that correlate with the piezoelectric response. 7,8,10,[47][48][49] In total, 53 materials (see supplementary materials) are included in our initial dataset, and the results for the piezoelectric response are summarized in Table 1. Notably, AlN doped with boron and scandium together shows a slight increase in the piezoelectric constant relative to AlN with scandium alone, which is currently attracting great interest. ...
While many piezoelectric materials are known, there is still great potential to improve on the figures of merit of existing materials through compositional doping, forming solid solutions. Specifically, it has been shown that doping and alloying wurtzite-structured materials can improve the piezoelectric response; however, a vast compositional space has remained unexplored. In this work, we apply a multi-level screening protocol combining machine learning, chemical intuition, and thermodynamics to systematically discover dopant combinations in wurtzite material space that improve the desired piezoelectric response. Through our protocol, we use computationally inexpensive screening calculations to consider more than 3000 possible ternary wurtzite solid solutions from 9 different wurtzite base systems: AlN, BeO, CdS, CdSe, GaN, ZnO, ZnS, ZnSe, and AgI. Finally, based on thermodynamic analysis and explicit piezoelectric response calculations, we predict 11 materials with improved piezoelectric response, due to the incorporation of electropositive dopants.
... Recent experimental and theoretical investigations have demonstrated a significant improvement for piezoresponse in the doped w-AlN [16][17][18][19]. The piezoelectric characterization of several co-doped AlN was described by Iwazaki et al It is found that the Mg-Hf co-doped can effectively enhance the piezoelectric coefficient d 33 of AlN by 260% [20]. Nguyen et al experimentally proved that the piezoelectric coefficient d 33 of Mg-Hf co-doped AlN could be improved by increasing co-doped concentration [21,22]. ...
... The previous research only investigated the piezoelectric properties of Mg-Hf co-doping concentrations below 25%, and they did not analyze the mechanism of piezoelectric properties [20][21][22]. To further improve the performance of AlN materials, several co-doped AlN structures with the same doping proportion of Mg-Hf (Mg x/2 Hf x/2 Al 1−x N) are proposed. ...
... The calculated results suggest the piezoelectric coefficient under doping concentration of x = 0.375 could be reached 16.417 pC/N, which is three times higher than AlN. Furthermore, when we compared the values obtained for x = 0, x = 0.125 and x = 0.250, d 33 showed a 1.6-fold and 2.7-fold increase, corresponding rather well to earlier reported theoretical and experimental results [20,22]. Therefore, the piezoelectric coefficient of materials can be altered by breaking the symmetry of crystal structure. ...
The piezoelectric coefficient of intrinsic AlN is not meeting the demand from some high-performance applications in MEMS compared with the commercialized piezoelectric ceramics. Therefore, we conducted a first principles calculation investigation of the piezoelectric properties of Mg-Hf co-doped AlN structures with the same doping proportion (Mg x/2Hf x/2Al1−x N) to further improve the performance of AlN materials. The analysis results suggested the co-doped structures show decreased band gap values with a non-symmetrical charges assignation. Consequently, both the elastic constant C 33 and Young’s modulus are largely reduced. Furthermore, the co-doped structure shows a drastically improved piezoelectric coefficient d 33 compared with intrinsic AlN.
... Despite intrinsically high sound velocity and great thermal conductivity, AlN films suffer from poor piezoelectric response and electromechanical coupling properties due to the local hexagonal symmetry of wurtzite crystal structure which makes polar bonds hard to rotate at room temperature, and the piezoelectric coefficients (d 33 ) were generally as low as 4.0-7.0 pC/N [7,[9][10][11][12][13], which significantly limits the FBAR performance in the practical applications of high-frequency mobile communications. The d 33 is typically determined by piezoelectric stress constant (e 33 ) and elastic constant (C 33 ) as governed by the equation d 33 ≈e 33 /C 33 [7]. ...
... Trolier-McKinstry et al., 2018;Park and Shrout, 1997). The development and use of elements and devices of functional electronics based on new piezo-and pyroelectric materials is currently an important and rapidly developing area of HF and microwave technology (Iwazaki et al., 2015;Hackenberger et al., 2019;Moreira et al, 2011). Among many different types of piezoelectric materials, quartz crystals are the most widely used traditional piezoelectric materials in practice (Mohammadi, 2015;Kotov et al., 2020). ...
An electroacoustic echo method for studying the high-frequency (HF) electrical and elastic properties of piezoelectric materials in a finely dispersed state is described. The characteristics and relaxation time of electroacoustic echo for natural and artificial quartz powders are determined. Natural one is represented by the following types: smoky quartz, citrine, amethyst, recrystallized, granular and columnar. It is shown that natural quartz (especially citrine), has a higher electromechanical coupling coefficient than artificial quartz. The amplitudes of HF electric field are determined, at which the saturation mode of the echo signals is observed.
... Moreover, the compatibility of complementary metal-oxide semiconductor (CMOS) fabrication to form monolithic devices has allowed for easy fabrication processes [14]. In addition, compared with materials such as PZT, its piezoelectric properties are weak; therefore, recent AlN developments include enhancement its piezoelectric properties, such as through doping with various metals, such as Sc [15,18], V [16], Ti [17], Ta [20], Mg [20], and others [20]. Among these metals, Sc stands out, and up to 40% of doped cases of Sc-doped AlN have been studied [18,19]; the piezoelectric properties have been found to increase by up to five times for the case of a 40% Sc-doping ratio. ...
Piezoelectric materials have attracted considerable attention over the last two decades because many technologies utilize their core properties of piezoelectric materials. Previous applications consisted of bulk structures; however, a shift towards better performance and a more simplified and compatible fabrication method are required. Aluminum nitride (AlN) is a material that fits these criteria; it has a non-centrosymmetric crystal structure with a polarized c-axis and exhibits piezoelectric properties. Furthermore, it has an added benefit as the fabrication process of AIN is compatible with complementary metal–oxide semiconductor technology. This has led to a rapid increase in the adoption and interest in AlN-based devices. In this review, the crystal structure of AlN and its piezoelectric properties are compared with those of aluminum scandium nitride. Subsequently, functional devices such as consumer-based devices, telecommunication-based devices, industrial-related applications, and medical applications are presented. Finally, a summary and discussion of the future AlN research are presented.
... However, the piezoelectric coefficient (d 33 ) of the pure AlN film is about 5.5 pc/N, the electromechanical coupling coefficient (k 2 eff ) is 6%$7% and that of corresponding SAW device is 2%, which are relatively low and limit the fractional bandwidth of the SAW RF filters [6,7]. Recent studies have found that doping the AlN with rare earth metals or transition metals can significantly improve its piezoelectric response and k 2 eff [8]. The k 2 eff of Sc x Al 1Àx N increases from 7% to 10% with the increase of the Sc contents. ...
Co-doping AlN film with various elements of rare earth or transition metals has been considered as a good method to significantly improve its piezoelectric responses of surface acoustic wave (SAW) devices. In this paper, we investigated the influences of different Er/Sc atomic percentage ratio on the piezoelectric and acoustic wave properties of the Er and Sc co-doped AlN films prepared by RF magnetron sputtering. Results show that c/a-axis ratio of the AlN films decreases after doped with Sc, whereas those of the AlN films co-doped with Er and Sc increase as the Er/Sc ratio increases. The reasons can be explained from the competitions of Sc and Er elements for occupying the Al atoms sites, and the larger ion radius of the Er compared that of Sc, which causes significant increase of c/a. Resonant frequency and Rayleigh wave velocity of the SAW resonators fabricated using these co-doped AlN films decrease as the Er/Sc ratio increases. Electromechanical coupling coefficient (k²eff) of the SAW devices increases after the AlN film is single doped with either Sc or Er element, but decreases after co-doping with both Er and Sc.
... † zarkadoulae@ornl.gov response by up to 40% [13][14][15][16][17][18] making these materials very attractive for practical usage. ...
We have performed first-principles calculations to investigate the electronic structure, configurations, formation, and binding energies of native and radiation induced point defects in pristine and Sc-doped wurtzite AlN. For the native defects, the nitrogen vacancy has the lowest formation energy in p-type material while the aluminum vacancy has the lowest formation energy in n-type material which is consistent with the previous studies. Several interstitial defect structures were modeled for Al, N, and Sc atoms. The effects of charge state on their relative stability were investigated. The binding energy of Sc with point defects was calculated and found to be dependent strongly on the defect type and charge state. The results obtained are discussed in light of the possible Sc effects on the radiation damage evolution in AlN. Thus the attraction of Sc atom to N vacancy and both Al and N interstitials reduces their mobility and increases Frenkel pair recombination distance.
... Enhancements comparable to the ones observed in ScAlN can be obtained by co-doping AlN with Mg and Nb (d 33 = 22 pm/V) [97]. Co-doping of AlN with Mg-Zr and Mg-Hf have also been proposed [98]. ...
Aluminum nitride (AlN) has gained wide interest owing to its high values of elastic modulus, band gap, dielectric strength, resistivity, thermal conductivity and acoustic velocities, especially because it retains most of its properties and versatility in the thin-film form. This review focuses on applications where the CMOS integration of AlN MEMS has been effectively demonstrated. First, the fundamental concepts of piezoelectricity on polycrystalline
$c$
-axis oriented thin-films are introduced and AlN is compared to other common piezoelectric materials, namely LiNbO
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, LiTaO
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, quartz, lead zirconate titanate (PZT), ZnO and GaN by thoroughly discussing the material properties, processing and technological implications. After presenting the possible MEMS-CMOS integration strategies, recent demonstrations of AlN-based devices are reviewed, namely energy harvesters, film bulk acoustic resonators (FBAR), contour mode resonators (CMR), gas sensors, imagers, microphones, transducers for chip-scale communication and calorimetric sensors. Finally, other recent applications/integration opportunities are outlined for AlN-based micro-mirrors, flexible sensors and transducers for liquid media and harsh environments. [2022-0006]
... 12,13 In addition, interest in AlN films on Si substrates has recently been increasing because of the piezoelectricity of AlN itself. 14,15 Sc-doped AlN exhibits ferroelectricity. 16 These applications also require a large-scale AlN film on a Si substrate. ...
The ability to control the polarity of an all-sputtered epitaxial GaN/AlN/Al film on a Si(111) substrate via intermediate oxidization was investigated. A stable surface of GaN on a Si substrate is a N-terminated surface (-c surface); hence, for electric device applications, the Ga-terminated surface (+c surface) is preferable. The GaN/AlN/Al film on Si(111) showed a -c surface, as confirmed by time-of-flight low-energy atom scattering spectroscopy (TOFLAS) and X-ray photoelectron spectroscopy (XPS). The AlN layer was intentionally oxidized via air exposure during film growth. The GaN surface subjected to the oxidization process had the +c surface. Secondary-ion mass spectrometry measurements indicated a high oxygen concentration after the intentional oxidization. However, the intentional oxidization degraded the crystallinity of the GaN/AlN layer. By changing the oxidization point and repeating the GaN/AlN growth, the crystallinity of GaN was recovered. Such polarity control of GaN on Si grown by sputtering shows strong potential for the fabrication of large-diameter +c-GaN template substrates at low cost.
