Based on density functional theory, we investigate the ferroelectric and piezoelectric properties of the AlN/ScN superlattice, consists of ScN and AlN buckled monolayers alternating along crystallographic c-direction. We nd that the polar wurtzite (w-ScAlN) structure is mechanically and dynamically stable, and is more stable than the nonpolar hexagonal at conguration. We show that ferroelectric polarization switching can be possible for epitaxially tensile strained superlattice. Due to the elastic constant C 33 softening along with an increase in e 33 , the piezoelectric coecient d 33 of the superlattice is doubled compared to pure w-AlN. The combined enhancement of Born eective charges (Z 33) and the sensitivity of the atomic coordinates to external strain (∂u 3 ∂η 3) is the origin of large piezoelectric constant e 33. Moreover, we show that epitaxial biaxial tensile strain signicantly enhances the piezo-response, so that d 33 becomes seven times larger than that of w-AlN at 4% strain. The tensile strain results in a huge enhancement in e 33 by increasing Z 33 and ∂u 3 ∂η 3 , which boosts the piezoelectric coecient. As short-period superlattice growth and epitaxial strain are already experimentally demonstrated in wurtzite nitrides, our results show a new more controlled approach

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Based on density functional theory, we show that Li andX (X=V, Nb and Ta) co-doping in 1Li:1X ratio broadens thecompositional freedom for significant piezoelectric enhancement in w-AlN, promising them to be good alternatives of expensive Sc. Interestingly, these co-doped w-AlN also show quite large spontaneous electric polarization about 0.80 C/m2 with the possibility of ferroelectric polarization switching, opening new possibilities in wurtzite nitrides. Increase in piezoelectric stress constant (e33) with decrease in elastic constant ( C33 ) results enhancement in piezoelectric strain constant ( d33 ), which is desired for improving the performance of resonators for high frequency RF signals. Also, these co-doped w-AlN are potential lead-free piezoelectric materials for energy harvesting and sensors as they improve the longitudinal electromechanical coupling constant (K^2 33), transverse piezoelectric strain constant (d31), and figure of merit for power generation. However, the enhancement in K^2 33 is not as pronounced as that in d33, because co-doping increases the dielectric constant. The longitudinal acoustic wave velocity (7.09 km/s) of Li0.1875Ta0.1875Al0.625N is quite comparable with that of commercially used piezoelectric LiNbO3 or LiTaO3 in special cuts (about 5~7 km/s) despite the fact that the acoustic wave velocities drop with co-doping or Sc concentration. File list (2)download file view on ChemRxiv codoped-AlN.pdf (0.93 MiB) download file view on ChemRxiv codoped-

This paper presents a method of integrating thick permanent magnetic films into a microfabrication process. An enhanced binding method consisting of a hybrid of Parylene N and Parylene C thin films was used in conjunction with various types of NdFeB powders to create embedded permanent magnet films. A systematic study of composite magnetic powders was developed using three different powders in order to control intrinsic coercivities (H ci ) and remanence (B r ) properties. In addition, four types of dispensing methods were investigated. A liquid dispensing method demonstrated the highest fill factor (79%) for a 400-µm-thick film with an enhanced remanence value of 0.59 T. A range of remanence values from 0.2 to 0.59 T were developed by varying the concentration of multiple magnetic powders within the composite material. Validation of the integrated magnetic material into a microelectromechanical system device was demonstrated through a polymer on a silicon cantilever structure.[ 2016-0073]Index Terms-Microelectromechanical systems (MEMS), integration, magnetic powders, bonded permanent magnets, Parylene.

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