On chip surge protection for GaN-power LEDs by ZnO thin film varistor

High ESD endurance capability is an important issue for the extensive application of power light emitting diodes (LEDs). Conventional ceramic varistor based on sintered bulk zinc oxide (ZnO) with various metal oxides as additives have widely used in surge protection device by grounding the excessive current for a long time. Those sintered bulk ZnO devices are known to exhibit high nonlinearity coefficient (α>50) and good reliability for many commercial applications. However, sintering manufacture method limits the practicability of integrating bulk ZnO varistor with other semiconductor devices. In this research, we report on the thin-film ZnO produced by sputtering system and post-heat treatment which have shown good varistor characteristics. The nonlinear coefficients (α) in the correspondent current -voltage (I-V) curve can up to 50 at a high electric field of 1.1 kV/cm, and, with efficiently resolving thermal generated by high injected current, this thin film varistor can conduct current to the density as high as 20A/cm² successfully. In addition, our thin film varistor devices combined with power LEDs by gold wires bonding revealed an improved electrostatic discharge (ESD) ability of up to 400V apparently. This wire bonding configuration will be modified to a flip-chip LED with the ZnO/Si submount in the future. Sputtering and annealing are two commonly used processes in general semiconductor manufacture procedures which are adopted in our ZnO thin film deposition. Therefore, our proposed method have provided a new possible solution to integrate not only LEDs but also other semiconductor devices with thin film varistor owning surge protection capability, especially to accomplish an on-chip surge protection.