GaN-based High Electron Mobility Transistors (HEMTs)

GaN-based high electron mobility transistor (HEMT) was developed under a CSIRsponsored project for bio-sensing applications.The device has a source-drain distance (Lsd) of 50 μm and a unit gate width of 2×125 μm and 2×50 μm. Various gateless and gated devices having Lsd variations from 7.0 μm to 50 μm are electrically tested to check the maximum drain current, breakdown voltage and transconductance values. The specific contact resistance of the order of 6 x 10-6 (Ω-cm2) is achieved which is near to the-stateof- the-art result. Schottky gate lengths down to 1.5 μm are defined using contact lithography. Finally, interconnects are structured. Fig. 1 shows onchip sensing using CSIR-CEERI developed GaNbased HEMTs-on-Sapphire. Channel current was measured on two types of devices having sourcedrain distance of 7 μm (1×125 μm) and 50 μm (2×125 μm) respectively. Recorded peak channel current values were 0.72 A/mm and 0.25 A/mm on the devices (without passivation), respectively, which met the targeted specifications. The two devices survived up to 20 V and 80 V, respectively. Fig. 2 shows the I-V characteristics of the device with a source-drain distance of 50 μm, which was best-suited for biosensing applications due to large source-drain distance. The device was passivated for sensing purpose using photoresist as well as a dielectric. Source-drain pads and channel areas are structured in the passivation layer for sensing. In the several iterations of sensing runs for salty water detection in the concentration range starting from millimolar to picomolar, the devices showed good response even for picomolar concentration as shown in Fig. 23.

Fig. 1: On-chip sensing using GaN-based HEMTs on Sapphire.

Fig. 2: On-chip sensing using GaN-based HEMTs on Sapphire.

Fig. 3: On-chip sensing using GaN-based HEMTs on Sapphire.