On Chip Surge Protection for GaN Power LEDs by ZnO Thin Film Varistor

摘要

High electrostatic discharge(ESD) endurance capability is an important issue for extensive applications of power light emitting diodes (LEDs). Conventional ceramic varistors, based on sintered bulk zinc oxide (ZnO), with various metal oxides as additives have been widely used in surge protection devices by grounding the excess current for a long time. Those sintered bulk ZnO devices are known to exhibit high nonlineariry coefficient (α□50) and good reliability for many commercial applications. However, the sintering manufacture method limits the practicability of integrating bulk ZnO varistor with other semiconductor devices. In this paper, we report on the thin-film ZnO produced by sputtering system and post-heat treatment which has shown good varistor characteristics. The nonlinear coefficients (a) in the corresponding current -voltage (I-V) curve can up to 50 at a high electric field of 1.1 kV/cm, With efficiently resolving thermal generated by high injected current, this thin film varistor can conduct current to the density as high as 20A/cm~2 successfully. In addition, we connected the ZnO varistor with GaN power LEDs by gold wire bonding. This structure revealed an improved electrostatic discharge (ESD) ability of up to 400V. 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 manufacturing procedures which are adopted in our ZnO thin film deposition. Therefore, our proposed method has provided a new possible solution to integrate not only LEDs but also other semiconductor devices with thin film varistor having surge protection capability, especially to accomplish an on-chip surge protection.