Acoustic wave sensors have numerous applications in physical, chemical and biological sensing. Among different types of acoustic wave sensors, Lamb-wave sensors are attractive for those applications because of excellent sensitivity, capability to function well in both liquid and gaseous environments, and scalability to be produced in a batch process. Traditionally, piezoelectric materials required for this type of sensors are based on sputtered or polycrystalline materials such as AlN, ZnO and lead zirconate titanate (PZT). Recently, single crystalline gallium nitride (GaN) is regarded as a good candidate for alternative sensing material. The advantageous properties of GaN include high acoustic velocities, a wide band gap of 3.4eV and the stability to operate in harsh environments....[ Read more ]

Acoustic wave sensors have numerous applications in physical, chemical and biological sensing. Among different types of acoustic wave sensors, Lamb-wave sensors are attractive for those applications because of excellent sensitivity, capability to function well in both liquid and gaseous environments, and scalability to be produced in a batch process. Traditionally, piezoelectric materials required for this type of sensors are based on sputtered or polycrystalline materials such as AlN, ZnO and lead zirconate titanate (PZT). Recently, single crystalline gallium nitride (GaN) is regarded as a good candidate for alternative sensing material. The advantageous properties of GaN include high acoustic velocities, a wide band gap of 3.4eV and the stability to operate in harsh environments.

In this study, Lamb-wave sensors were designed, fabricated with MOCVD-grown GaN-based thin films on silicon substrates and further developed into a universal platform for physical and biological sensing ranged from a microbalance (mass sensor) and a UV light sensor to a specific protein sensor. Techniques of fabricating membrane sensors were developed and refined to optimize the sensor performance and yield.

Experiments were performed to demonstrate the various sensing capability. Good results were obtained including a high mass sensitivity (274 cm²/g), a low limit of detection (LOD) of UV intensity (4.1 μW/cm²)and a crisp signal response at low concentration of anti-bovine serum albumin (1 μg/ml).

The novelty of using GaN thin films on a silicon substrate not only allows for a variety of high-performance sensors to be fabricated on a general platform, but also enables generic GaN-based devices to be integrated on a chip in the future, i.e., systems-on-a-chip (SoC). Potential devices for integration include well-developed GaN-based high electron mobility transistor (HEMT) circuits, light emitting diodes (LED), as well as power and RF devices.