Hybrid semiconductor-piezoacoustic radiofrequency device
An amplifying radiofrequency device includes a piezoelectric film and a semiconductor amplifier layer. The piezoelectric film is conformed as an acoustic waveguide. The piezoelectric film has a principal acoustic propagation direction parallel to the principal conduction direction of the amplifier layer. Interdigitated transducers are positioned on the piezoelectric film to respectively launch an acoustic wave in response to an input RF signal, and transduce the acoustic wave back to an output RF signal. There is a distance of less than the acoustic wavelength between the semiconductor amplifier layer and the piezoelectric film. The piezoelectric film has a thickness of less than the acoustic wavelength. According to a method for making such a device, a stack of III-V layers is epitaxially grown on a III-V substrate, wherein the stack comprises a first etch stop layer, a second etch stop layer, an amplifier layer, and a contact layer. The stack is bonded to a lithium niobate film. The III-V substrate is removed by etching down to the first etch stop layer. Deposition windows are opened by etching from the first etch stop layer down to the contact layer. Metal contact electrodes are deposited in the deposition windows.
1. An amplifying radiofrequency (RF) device, comprising a piezoelectric film conformed as an acoustic waveguide having a principal acoustic propagation direction and a semiconductor amplifier layer positioned near the piezoelectric film and having a principle conduction direction parallel to the principal acoustic propagation direction, wherein:
the device further comprises an input interdigitated transducer (IDT) positioned on the piezoelectric film and conformed to launch an acoustic wave having a wavelength λ into the piezoelectric film in response to an input RF signal;
the device further comprises an output interdigitated transducer (IDT) positioned on the piezoelectric film and conformed to intercept the launched acoustic wave and convert it to an output RF signal;
the semiconductor amplifier layer is distant from the piezoelectric film by less than k; and
the piezoelectric film has a thickness of less than λ.
2. The device of claim 1 , wherein the piezoelectric film is suspended such that an air gap separates it from the semiconductor amplifier layer.
3. The device of claim 1 , wherein the piezoelectric film and the semiconductor amplifier are suspended such that an air gap at least partially separates them from a substrate.
4. The device of claim 1 , wherein the piezoelectric film has a width less than λ in a direction perpendicular to both its thickness and its principal acoustic propagation direction.
5. The device of claim 1 , wherein the piezoelectric film comprises lithium niobate.
6. The device of claim 1 , wherein the piezoelectric film comprises aluminum nitride.
7. The device of claim 1 , wherein the semiconductor amplifier layer is an epitaxial III-V film.
8. The device of claim 1 , conformed as a monolithic device in which the piezoelectric film and the semiconductor amplifier layer are in direct contact without an intervening bonding layer.
9. The device of claim 1 , wherein a piezoelectric film of lithium niobate is bonded by a bonding layer to a semiconductor amplifier layer of epitaxial indium arsenide.
10. The device of claim 1 , wherein a piezoelectric film of lithium niobate is bonded by a bonding layer to a semiconductor amplifier layer of epitaxial indium gallium arsenide.
11. The device of claim 1 , wherein a piezoelectric film of lithium niobate is bonded by a bonding layer to a semiconductor amplifier layer of epitaxial indium gallium arsenide having a conductivity-thickness product of less than 100 μmho-cm.
12. The device of claim 1 , wherein a piezoelectric film of aluminum nitride is monolithically bonded to a semiconductor amplifier layer of silicon.
13. The device of claim 1 , wherein:
a piezoelectric film of aluminum nitride is monolithically bonded to a silicon substrate;
the silicon substrate comprises a background region and a semiconductor amplifier region;
the background region has a doping level of 4×10 14 cm −3 or less; and
the semiconductor amplifier region has a doping level of 4×10 15 cm −3 or more.