III-V nitride resonate based photoacoustic sensor
The invention relates to a micro cantilever beam sensor and making method, including a chip, and its character: there is at least a group of sensor cells set on the chip, where the sensor cell is composed of the completely same four force-sensitive resistors composing a Wheatstone bridge and two cantilever beams, two of these resistors are on the substrate of the chip, the other two are on the two cantilever beams, respectively, one cantilever beam acts on a measuring cantilever beam and the other one acts on a reference cantilever beam, and the measuring cantilever beam is set with a sensitive layer on the surface. It can design and prepare in a liquid-flow micro-tank by front etching and silicon-glass bonding techniques, to directly detect liquid biomolecule. Whether applied to gas sensor or biosensor, it will play an important role in reducing device size, enhancing device sensitivity and realizing sensor multi-functionality. It has wide prospects for the fields of environment monitoring, clinic diagnosis and therapy, new drug development, food safety, industrial processing control, military and so on.
1. A method of fabricating a GaN cantilever for a photoacoustic sensor from a wafer, wherein the wafer comprises a substrate, a buffer layer on the substrate, and a first undoped GaN layer on the buffer layer, the method comprising:
forming a mesa comprising an AlGaN layer over a portion of the wafer;
defining a cantilever outline in the first undoped GaN layer, wherein the mesa is positioned near or on the base of the cantilever outline;
depositing at least two contacts onto the mesa; and
through backside etching, removing the wafer in an area of the cantilever outline to release the cantilever,
wherein the cantilever has integrated near or at the base of the cantilever a heterojunction field-effect transistor (HFET) deflection transducer, wherein the HFET deflection transducer has a cross-section comprising the following layers arranged in consecutive horizontal order:
the buffer layer directly on the substrate;
the first undoped GaN layer directly on the buffer layer;
an AlN layer directly on the first undoped GaN layer;
the AlGaN layer directly on the AlN layer; and
an additional undoped GaN layer directly on the AlGaN layer.
2. The method of claim 1 , further comprising: forming, through etching, microchannels and a reservoir within the first undoped GaN layer near the mesa.
3. The method of claim 2 , further comprising: coating the microchannels and the reservoir with a poly(p-xylylene) polymer.
4. The method of claim 2 , further comprising: encapsulating the microchannels and the reservoir by securing a sapphire window thereto.
5. The method of claim 2 , further comprising: encapsulating the cantilever with a sapphire window such that the cantilever is positioned within an enclosed space.
6. The method of claim 5 , further comprising: forming a vacuum within the enclosed space so as to maintain a vacuum around the cantilever.
7. The method of claim 1 , wherein the substrate comprises silicon.
8. The method of claim 1 , wherein the cantilever is fabricated with a length of from 50 μm to 300 μm, a width of from 25 μm to 100 μm, and a thickness of from 0.5 μm to 1.5 μm.
9. The method of claim 1 , wherein the substrate comprises silicon, and wherein the buffer layer has a thickness from 0.5 μm to 2.5 μm, and further wherein the first undoped GaN layer has a thickness from 500 nm to 2 μm.
10. The method of claim 1 , wherein the cantilever for a photoacoustic sensor is fabricated to have a gauge factor greater than 4500.