Multiple layer system, method of manufacture and saw device formed on the multiple layer system
A layer system especially for forming SAW devices thereon is proposed comprising a monocrystalline sapphire substrate having a first surface and a crystalline piezoelectric layer comprising MN, deposited onto the first surface, and having a second surface. As a first surface a crystallographic R-plane of sapphire is used enabling an orientation of c-axis of the piezoelectric layer parallel to the first and second surfaces.
1. A layer system comprising:
a monocrystalline sapphire substrate having a first surface;
a crystalline piezoelectric layer comprising an aluminum nitride (AlN), grown epitaxially on the first surface, and having a second surface facing away from the first surface;
wherein the first surface is a crystallographic R-plane of sapphire;
wherein the epitaxial relationship between the monocrystalline sapphire substrate and the crystalline piezoelectric layer is as follows:
a (11-20)-plane of the crystalline piezoelectric layer (x-cut) is parallel to a (1-102)-plane of the monocrystalline sapphire substrate (R-plane),
an in-plane [1-100]-direction of the crystalline piezoelectric layer is parallel to a [−1-120]-direction of the monocrystalline sapphire substrate, and
an in-plane [000-1]-direction (crystallographic c-axis) of the crystalline piezoelectric layer is parallel to a [1-10-1]-direction of the monocrystalline sapphire substrate.
2. The layer system of claim 1 , wherein the crystalline piezoelectric layer comprises the AlN doped with a dopant that improves piezoelectric coupling.
3. The layer system of claim 2 , wherein the crystalline piezoelectric layer comprises c-axis oriented aluminum scandium nitride (AlScN), and wherein an amount of dopant scandium (Sc) contained in the crystalline piezoelectric layer is between 5 and 45 at %.
4. The layer system of claim 1 , wherein the crystalline piezoelectric layer comprises the AlN doped with scandium (Sc), and wherein a seed layer of pure AlN is arranged between the monocrystalline sapphire substrate and the crystalline piezoelectric layer of scandium doped aluminum nitride (AlScN).
5. The layer system of claim 1 , comprising a layer of silicon dioxide (SiO2) deposited onto the second surface.
6. A surface acoustic wave (SAW) device comprising the layer system of claim 1 and having an interdigital electrode structure arranged on top of the second surface.
7. The SAW device of claim 6 , wherein the interdigital electrode structure is adapted to excite a SAW in the crystalline piezoelectric layer having a given wavelength λ, ≤wherein a thickness dP of the crystalline piezoelectric layer is chosen according to a relation 0.3λ≤d P ≤3λ.
8. The SAW device of claim 6 , wherein the first surface is tilted against the R-plane by an angle δ of 0.5° to 6°.
9. The SAW device of claim 6 , wherein the interdigital electrode structures have an in-plane orientation with a rotation angle between 0° and 90° around a surface normal.
10. The SAW device of claim 6 , wherein the interdigital electrode structure comprises copper (Cu) and/or aluminum (Al).
11. The SAW device of claim 6 , comprising further functional layers chosen from a group of a passivation layer, a trimming layer of silicon nitride (SiN) and a temperature compensation layer.