This paper will present the concluding results of a comprehensive study aimed at developing a model for predicting the overall reliability of an asymmetric thermal actuator. This actuator is designed for co-packaged use as a variable optical attenuator (VOA) within a 10 Gbps optical receiver. This paper will address the limitations of a previously reported vision recognition system. It is shown that the electrical resistance change correlates well with the displacement change over time, and as a result, simple in-situ resistance monitoring for degradation detection can easily be realized. The novel methodology employed to estimate the lifetime performance of the MEMS VOA is also presented; whereby, the accelerated ageing wearout model derived from 93,600 device hours is combined with the module characteristics, and all associated error coefficients in a Monte Carlo simulation. Simulation results will provide the end user with a 3 sigma confidence prediction of the receiver over-life attenuation curve and all end of life conditions associated with the MEMS component. It will be demonstrated that when designed properly, a thermal actuator will provide predictable accurate and reliable stability over life.
In this work we investigate the use of low-frequency noise (LFN) spectroscopy as a sensitive tool for investigation of semiconductor avalanche photodiode (APD) quality and reliability for high-speed communication applications. Samples from several manufacturing runs pre-screened through the standard production batch validation showed very low start of life low-frequency noise levels. The LFN test indicates the high quality of the devices with respect to noise characteristics. We also investigated the noise characteristics of production reject devices, some of which exhibit a 1/<i>f</i> type noise peak at the guard ring punch-through voltages, and an increase in noise intensity at punch-through voltages after long term accelerated lifetesting (>1000 h at 200°C and 100 μA). Useful information on device quality can thus be obtained from the noise measurement results performed in the deep breakdown bias range (27-30 V), where a sharp peak of the Lorentzian type noise may be observed. This feature is believed to be due to intensive recombination processes at defects in interlayer regions. It is also shown that avalanche photodiodes containing some defects exhibit not only increased dark current and low-frequency noise level, but also increased multiplication excess noise factor which decreases with increasing input light intensity. This work shows that LFN spectroscopy is very useful for the localization of noise sources, and provides important information for further product quality improvement.
Light-current, relative intensity noise and spectral characteristics of a group of gain-guided InGaAsP/InP MQW buried heterostructure laser diodes have been investigated under accelerated aging conditions. The operating current, I<sub>op</sub>, at constant output optical power increases logarithmically with time in stable devices, which indicates that the life expectancy of the lasers exceeds 2x10<sup>5</sup> hours or greater than 20 years. The emitted light wavelength at constant output power shifts by 2-2.5Å during 3000 hours of overstressing, mainly due to the increase in I<sub>op</sub>. High-frequency RF signal-induced transient chirp for relative stable LDs at constant output power shows very little change with time.
A detailed study of both the optical and electrical low-frequency noise and correlation factor between optical and electrical fluctuation characteristics of single-mode multiple quantum wells (MQW) curied-heterostructure (BH) distributed feedback (DFB) laser diodes has been carried out under a wide current range. These techniques have been used to assess the structural differences between devices that exhibit superior and poor performance and reliability. It has been concluded that for the devices investigated here, the poor device performance characterstics (larger threshold current) and poor reliability are induced by the existence of defects in the interface between the active region and burying laser. These defects generate leakage currents that lead to teh larger threshold current. Defects migration during ageing forms clusters, and this leads to the poor reliability of the lasers. We demonstrate that the low-frequency noise investigations can detect the presence of defects that induce short device lifetime.
This paper describes a test system and presents preliminary results of a long-term reliability study of an electro-thermally actuated integrated MEMS optical attenuator. These tests are designed to address the specific failure modes and life prediction models required for "set and forget" components and to identify deficiencies that exist in the current telecom (Telcordia) testing standards as they apply to MEMS. The failure modes are activated by overstressing the devices to a much higher power than would be observed under normal operating conditions. The paper describes a multi-module experimental test station for exciting devices at up eight different power levels, both AC and DC. At set intervals devices are tested off-board to measure changes in actuator deflection and resistance over time. The preliminary results show that devices start to degrade at power levels 92% over operating power after 400 hours of stress.
We have performed a structural study of GaAlAs/GaInAs lasers, designed to emit at 980 nm, ass they undergo catastrophic optical damage (COD) during L-I testing. Electron beam induced current analysis shows that COD is characterized by the introduction of high densities of extended defects along the cavity of the laser, in the vicinity of the output facet of the device. Having determined the approximate location of the induced defects, we have employed precision transmission electron microscope specimen fabricating techniques to study the structure of the defects in detail. Dislocation loops ranging from < 10 nm to > 100 nm in diameter are observed in the modal region of the degraded lasers. The heterostructure comprising the active region of the device is interdiffused in regions of the highest defect density, and in some regions, melting of the laser cavity is observed. A `fast capture' laser degradation analysis technique has been developed, which allows us to examine the infant stages of COD failure. These experiments clearly demonstrate that the COD damage initiates exactly at the laser facet, and propagates back along the cavity with continued device stressing. The highest output power level which can be attained is limited by the thermal characteristics of the device. Higher power levels can be attained under pulsed operation, through which `thermal rollover' conditions are avoided. COD failure under pulsed operation results in a dramatically altered defect distribution consisting of periodic arrays of dislocation tangles along the laser cavity. The periodicity of these defective `packets' is related to the magnitude of the drive current pulse at the time of failure.