Piezo-TFT cantilever MEMS
A piezo-TFT cantilever microelectromechanical system (MEMS) and associated fabrication processes are provided. The method comprises: providing a substrate, such as glass for example; forming thin-films overlying the substrate; forming a thin-film cantilever beam; and simultaneously forming a TFT within the cantilever beam. The TFT is can be formed least partially overlying a cantilever beam top surface, at least partially overlying a cantilever beam bottom surface, or embedded within the cantilever beam. In one example, forming thin-films on the substrate includes: selectively forming a first layer with a first stress level; selectively forming a first active Si region overlying the first layer; and selectively forming a second layer overlying the first layer with a second stress level. The thin-film cantilever beam is formed from the first and second layers, while the TFT source/drain (S/D) and channel regions are formed from the first active Si region.
1. A piezo thin-film transistor (piezo-TFT) cantilever microelectromechanical system (MEMS), the piezo-TFT cantilever comprising:
a substrate;
a thin-film cantilever beam having a distal end, anchored to the substrate, and a proximal end;
a TFG within the cantilever beam;
wherein the cantilever beam includes:
a first thin-film layer with a first stress level; and
a second thin-film layer with a second stress level overlying the first layer.
2. The piezo-TFT cantilever of claim 1 wherein the cantilever beam has a top surface and a bottom surface; and
wherein the cantilever TFT has a location selected from the group including at least partially on the cantilever beam top surface, at least partially on the cantilever beam bottom surface, and embedded within the cantilever beam.
3. The piezo-TFT cantilever of claim 1 wherein the cantilever beam and TFT are made from materials selected from the group including amorphous silicon (a-Si), polycrystalline Si (poly-Si), oxides, a-SiGe, poly-SiGe, metals, metal-containing compounds, nitrides, polymers, ceramic films, magnetic films, and compound semiconductor materials.
4. The piezo-TFT cantilever of claim 1 wherein the substrate is a material selected from the group including glass, polymer, quartz, metal foil, Si, sapphire, ceramic, and compound semiconductor materials.
5. The piezo-TFT cantilever of claim 1 further comprising:
a temporary sacrificial layer overlying the substrate; and
a cavity formed between the first layer and the substrate in response to removing the temporary sacrificial layer.
6. The piezo-TFT cantilever of claim 5 wherein the temporary sacrificial layer is a material selected from the group including AlN, Si, SiGe, polymers, dielectrics, and ceramics.
7. The piezo-TFT cantilever of claim 1 wherein the first and second layers are a material selected from the group including Si, Si nitride, and Si oxide.
8. The piezo-TFT cantilever of claim 1 wherein the cantilever TFT is a cantilever strain-sensing TFT; and
the piezo-TFT cantilever further comprising:
a strain-reference TFT overlying the substrate and adjacent the cantilever beam.
9. The piezo-TFT cantilever of claim 1 wherein the cantilever TFT includes a channel region and source/drain regions formed in an active Si region; and
wherein the TFT active Si region is part of a cantilever beam Si layer.
10. The piezo-TFT cantilever of claim 1 wherein the cantilever TFT includes a channel region and source/drain regions formed in an active Si region; and
wherein the TFT active Si region and the cantilever beam include laser annealed materials.
11. The piezo-TFT cantilever of claim 1 further comprising:
a strain-reference TFT;
a sacrificial layer overlying the substrate with temporary regions and permanent regions; and
a cavity formed between the first layer and the substrate in response to removing the temporary sacrificial layer;
wherein the cantilever TFT is a strain-sensing TFT that overlies the cavity; and
wherein the strain-reference TFT overlies the permanent region of sacrificial layer.