Investigation of thin film varistor for GaN-based light-emitting diode electro static discharge protection application
Date Issued
2007
Date
2007
Author(s)
Cheng, Kai-Wen
DOI
zh-TW
Abstract
In recent years, there is a large improvement on the luminous efficiency of LEDs. However, there are some problems in LED ESD protection. Generally, there are two technologies to do the LED ESD protection. One is parallel LED with the head-to-head Zener diodes, the other is parallel LED with a reverse connected diode which is due to the property that LEDs only have troubles in the reverse-bias operation. The disadvantage of the first technology is needed extra works to fabricate the Zener diodes. The disadvantage of the second technology is that the extra fabricated diodes will occupy some emitting areas on the LED wafer. So we want to investigate thin film varistor, since thin film process is simpler than traditional ceramic process, and it is easy to integrate into semiconductor process.
In the experiment, we sputter Si/ZnO on sapphire substrate, and do the I-V measurement, optical transmittance measurement and post-annealing process. It is found that the conductance and the optical transmittance of thin film become higher after doing the post-annealing process. It is note that the Si/ZnO thin film demonstrate the “varistor-like” characteristic after the post annealing process at 1100℃ for 30 secs in air condition. The optical transmittance of thin film will increase about three times after the post annealing process. Comparing the I-V characteristic of the sample on which the post annealing is carried out with that of regular LED chip at 20mA, it is found that the sample will turn on at ±5V. Relatively, the samples have low resistance at high voltage, and they have high resistance at low voltage. It seems to have “varistor-like” behavior and it provides another current path for electro-static discharge. It is a possible method to do the LED ESD protection.
Subjects
變阻器
靜電防護
氧化鋅
薄膜變阻器
發光二極體
LED
varistor
ESD
thin film varistor
ZnO
Type
thesis
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