Study on degradation of propagation delay time and low-frequency noise of high-speed optocoupler

Abstract

CTR (Current transfer ratio) is generally used to characterize the reliability parameters of optocoupler in engineering. However, high-speed optocoupler has a different structure from the common optocoupler, therefore its most important parameter should be propagation delay time. In addition, CTR serving as the macroscopic parameters, its changes can’t directly reflect microscopic changes of the internal defects in device. It is discovered that the number of microscopic defects in the device and the level of low-frequency noise shows a positive correlation. In terms of high-speed optocoupler, this paper proposed a method of combining propagation delay time and low-frequency noise to evaluate the storage reliability. The paper demonstrated how to design circuit to test these parameters and obtain their variations trajectory in accelerated degradation test. In this paper, 20 VO2630 devices were divided into four groups, and a accelerated test at 100°C, 125°C, 150°C and 175°C was conducted to monitor propagation delay time and other parameters related with low-frequency noise. These parameters had different degrees of degradation. This paper showed the degradation process of propagation delay time. It was found that the initial value of propagation delay time was nearly identical, but parameters related with low-frequency noise had different initial values. The larger the initial value of low frequency noise is, the faster propagation delay time will degrade. The main cause of degradation of propagation delay time is Schottky clamped transistor degradation. Finally, this paper discussed the advantages and disadvantages about utilizing conventional electrical parameters or low frequency noise to evaluate the reliability.