Manufacturing process for thin film bulk acoustic resonator (FBAR) filters
View Patent ↗Method for fabricating an acoustical resonator on a substrate having a top surface. First, a depression in said top surface is generated. Next, the depression is filled with a sacrificial material. The filled depression has an upper surface level with said top surface of said substrate. Next, a first electrode is deposited on said upper surface. Then, a layer of piezoelectric material is deposited on said first electrode. A second electrode is deposited on the layer of piezoelectric material using a mass load lift-off process.
1. A method for fabricating an acoustical resonator on a substrate having a top surface, said method comprising steps of:
generating a depression in said top surface;
filling said depression with a sacrificial material, said filled depression having an upper surface level with said top surface of said substrate;
depositing a first electrode on said upper surface;
depositing a layer of piezoelectric material on said first electrode;
depositing a second electrode on said layer of piezoelectric material by employing a mass load lift-off process, wherein the mass load lift-off process further comprises:
forming a mass-loading pattern over the second electrode, and depositing a mass-loading layer over the second electrode; and
removing said sacrificial material from said depression.
2. The method of claim 1 wherein the step of depositing a first electrode on said upper surface comprises the steps of:
depositing a seed layer;
depositing a conductive material;
applying a patterned mask;
etching the conductive material and seed layer in accordance with the patterned mask to form a bottom electrode.
3. The method of claim 1 further comprising:
depositing a passivation layer for protecting the second electrode.
4. The method of claim 1 wherein said sacrificial material comprises a material chosen from the group consisting of PSG, BPSG, spin-on-glass, polyvinyl, polypropylene and polystyrene.
5. The method of claim 1 wherein said step of filling said depression comprises the steps of:
depositing a layer of said sacrificial material over said depression;
planarizing said deposited layer; and
polishing said planarized layer.
6. The method of claim 1 further comprising the step of providing a layer of an electrically insulating material on the surface of said substrate and depression prior to depositing said layer of sacrificial material, said electrically insulating material preventing a diffusion of elements in said sacrificial material from diffusing into said substrate.
7. The method of claim 1 wherein said first electrode comprises molybdenum.
8. The method of claim 1 wherein said layer of piezoelectric material comprises AlN.