In a first step of a method for producing a transparent AlN sintered body, first, a formed body is prepared by forming a mixture obtained by mixing a sintering aid with an AlN raw-material powder containing a plate-like AlN powder whose plate surface is a c-plane and which has an aspect ratio of 3 or more. At this time, the mixture is formed such that the plate surface of the plate-like AlN powder is disposed along a surface of the formed body. In a second step, an oriented AlN sintered body is obtained by subjecting the formed body to hot-press sintering in a non-oxidizing atmosphere while applying a pressure to the surface of the formed body. In a third step, a transparent AlN sintered body is obtained by sintering the oriented AlN sintered body at normal pressure in a non-oxidizing atmosphere to remove a component derived from the sintering aid.

A piezoelectric material comprises AlN doped with cations of one or more elements selected from the group consisting of: one of Sb, Ta, Nb, or Ge; Cr in combination with one or more of B, Sc, Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, or Yb; one of Nb and Ta in combination with one of Li, Mg, Ca, Ni, Co, and Zn; Ca in combination with one of Si, Ge, Ti, Zr, and Hf; Mg in combination with one of Si, Ge, and Ti; and one or more of Co, Sb, Ta, Nb, Si, or Ge in combination with one or more of Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, or Yb. The cations at least partially substitute for Al in the crystal structure of the piezoelectric material.

A piezoelectric material comprises AlN doped with cations of one or more elements selected from the group consisting of: one of Sb, Ta, Nb, or Ge; Cr in combination with one or more of B, Sc, Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, or Yb; one of Nb and Ta in combination with one of Li, Mg, Ca, Ni, Co, and Zn; Ca in combination with one of Si, Ge, Ti, Zr, and Hf; Mg in combination with one of Si, Ge, and Ti; and one or more of Co, Sb, Ta, Nb, Si, or Ge in combination with one or more of Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, or Yb. The cations at least partially substitute for Al in the crystal structure of the piezoelectric material.

A MEMS structure may include a substrate, a first metal layer arranged over the substrate, an aluminum nitride layer at least partially arranged over the first metal layer and a second metal layer including one or more patterns arranged over the aluminum nitride layer. The first metal layer may include an electrode area configured for external electrical connection and one or more isolated areas configured to be electrically isolated from the electrode area and further configured to be electrically isolated from external electrical connection. Each pattern of the second metal layer may be arranged to at least partially overlap with one of the isolated area(s) of the first metal layer.

A MEMS structure may include a substrate, a first metal layer arranged over the substrate, an aluminum nitride layer at least partially arranged over the first metal layer and a second metal layer including one or more patterns arranged over the aluminum nitride layer. The first metal layer may include an electrode area configured for external electrical connection and one or more isolated areas configured to be electrically isolated from the electrode area and further configured to be electrically isolated from external electrical connection. Each pattern of the second metal layer may be arranged to at least partially overlap with one of the isolated area(s) of the first metal layer.

An aluminum nitride particle including: a plurality of planes randomly arranged in a surface of the particle, the plurality of planes forming an obtuse ridge part or an obtuse valley part in the surface of the particle, the plurality of planes being observable in a scanning electron micrograph with 500 times magnification; wherein the particle has a longer diameter L of 20 to 200 μm; a ratio L/D of the longer diameter L (unit: μm) to a shorter diameter D (unit: μm) of the particle is 1 to 1.25; and the plurality of planes comprise a first plane, wherein an area S (unit: μm.sup.2) of the first plane satisfies S/L≥1.0 μm.

An aluminum nitride particle including: a plurality of planes randomly arranged in a surface of the particle, the plurality of planes forming an obtuse ridge part or an obtuse valley part in the surface of the particle, the plurality of planes being observable in a scanning electron micrograph with 500 times magnification; wherein the particle has a longer diameter L of 20 to 200 μm; a ratio L/D of the longer diameter L (unit: μm) to a shorter diameter D (unit: μm) of the particle is 1 to 1.25; and the plurality of planes comprise a first plane, wherein an area S (unit: μm.sup.2) of the first plane satisfies S/L≥1.0 μm.

In various embodiments, controlled heating and/or cooling conditions are utilized during the fabrication of aluminum nitride single crystals and aluminum nitride bulk polycrystalline ceramics. Thermal treatments may also be utilized to control properties of aluminum nitride crystals after fabrication.

Provided is a piezoelectric thin film device containing: a first electrode layer; and a piezoelectric thin film. The first electrode layer contains a metal Me having a crystal structure. The piezoelectric thin film contains aluminum nitride having a wurtzite structure. The aluminum nitride contains a divalent metal element Md and a tetravalent metal element Mt. [Al] is an amount of Al contained in the aluminum nitride, [Md] is an amount of Md contained in the aluminum nitride, [Mt] is an amount of Mt contained in the aluminum nitride, ([Md]+[Mt])/([Al]+[Md]+[Mt]) is 36 to 70 atom %. L.sub.ALN is a lattice length of the aluminum nitride in a direction that is approximately parallel to a surface of the first electrode layer with which the piezoelectric thin film is in contact, L.sub.METAL is a lattice length of Me in a direction, and L.sub.ALN is longer than L.sub.METAL.

Provided is a piezoelectric thin film device containing: a first electrode layer; and a piezoelectric thin film. The first electrode layer contains a metal Me having a crystal structure. The piezoelectric thin film contains aluminum nitride having a wurtzite structure. The aluminum nitride contains a divalent metal element Md and a tetravalent metal element Mt. [Al] is an amount of Al contained in the aluminum nitride, [Md] is an amount of Md contained in the aluminum nitride, [Mt] is an amount of Mt contained in the aluminum nitride, ([Md]+[Mt])/([Al]+[Md]+[Mt]) is 36 to 70 atom %. L.sub.ALN is a lattice length of the aluminum nitride in a direction that is approximately parallel to a surface of the first electrode layer with which the piezoelectric thin film is in contact, L.sub.METAL is a lattice length of Me in a direction, and L.sub.ALN is longer than L.sub.METAL.