Oxide VCSELs are the emitter of choice for high-speed optical communication applications. A low divergence circular beam, wafer-level testing and the capability to create dense two-dimensional arrays provide the VCSEL with unique advantages over edge emitting lasers, such that VSCELs have become a significant part of the optical communication market. An equally important metric for VCSELs is field reliability since significant failure rates are unacceptable for implementation of reliable networks.
In order to better understand potential failure paths of VCSELs during field use, a variety of failures have been intentionally created on oxide VCSELs made from AlGaAs / GaAs materials operating at 850nm. Failures were created with epitaxial defects, scratches, surface contamination, thermal shock , ESD and elevated temperature and humidity (85C/85% humidity). We will present the results of these intentional failures, assess high-probability failure paths and compare and contrast the various failure mechanisms.
Suning Xie, Robert Herrick, Gregory De Brabander, Wilson Widjaja, Uli Koelle, An-Nien Cheng, Laura Giovane, Frank Hu, Mark Keever, Tim Osentowski, Scott McHugo, Myrna Mayonte, Seongsin Kim, Danielle Chamberlin, S. Jeffrey Rosner, Grant Girolami
High speed fiber optic transceiver modules using parallel optics require that oxide-confined vertical-cavity surface-emitting lasers (VCSELs) be moisture resistant in non-hermetic environments. Conventional storage 85/85 (85°C and 85% relative humidity) testing without a bias does not adequately characterize oxide VCSEL’s moisture resistance. Oxide VCSELs do not fail or degrade significantly under such conditions. With a bias, however, we have found that moisture can cause failure modes not seen in dry reliability testing. Without proper device design and fabrication, these failure modes lead to high failure rates in oxide VCSELs. In this paper, we first discuss the failure mechanisms we have identified, including dense dislocation network growth, semiconductor cracking and aperture surface degradation, all in high humidity and high temperature under operating conditions. We then report the results of environmental reliability tests on Agilent’s oxide VCSELs developed for the parallel optics modules. The results from a large number of wafers produced over an extended period of time have shown consistent, robust environmental reliability.
Joachim Krueger, Reena Sabharwal, Scott McHugo, Kimanh Nguyen, Ningxia Tan, Naginder Janda, Myrna Mayonte, Mike Heidecker, David Eastley, Mark Keever, Christopher Kocot
Electrostatic Discharge (ESD) damage is considered to be the leading cause for IC field failures. With increasing integration densities, devices tend to become more and more sensitive to ESD events. This observation holds in particular true for 850nm VCSELs, as the quest for higher modulation frequencies calls for shrinking device dimensions and aperture sizes in particular.
This publication is geared towards an understanding of the various factors that lead to ESD-related failures of oxide VCSELs. A broad variety of current VCSEL product lines at Agilent have been investigated in respect to their ESD resistance and related long-term reliability. Intentionally stressed devices have been characterized in terms of their electrical, optical and visual failure patterns as well as the medium time-to-failure. Cross-sectional and plan-view TEM have been employed to localize ESD damage and its propagation. For the first time, emission microscopy has been used to study the electroluminescence pattern of damaged VCSELs at very low currents. The paper will conclude by listing experimental signatures allowing for differentiation between ESD and other failure modes. Based upon these, effective screening methods are proposed.
With the development of high quality x-ray mirrors and x-ray zone plates, the use of micron-size x-ray beams is growing rapidly. The size of the focal spot is frequently characterized by measuring either the transmitted or fluorescence counting rate as a knife edge is scanned through the beam; the full width half maximum (FWHM) of the derivative of this scan is often quoted as the 'resolution' of the system. Many systems have been built which are claimed to have a focal spot size of 1 micrometer2 or less. Unfortunately, this parameter does not give an accurate presentation of the focal quality of the beam. We have developed a test using a pattern of microfabricated 'dots' on a silicon wafer to measure the encircled energy in an x-ray focal spot as a function of radius. Using this test, we have found that focused x-ray beams frequently have a large, low intensity flare that is not represented in the beam profile as measured by the knife edge scan method. This flare can be produced by several factors including diffuse scattering from the mirror surfaces and higher orders of a zone plate. It can cause serious errors in when calculating elemental concentrations in heterogeneous samples. In addition, for micro-XAS experiments where the energy is scanned to identify the compound at a particular point, this flare may vary as a function of energy and therefore change the XAS spectra from a small particle in a complex sample.
Conference Committee Involvement (1)
High and Low Concentrator Systems for Solar Electric Applications IV
3 August 2009 | San Diego, California, United States
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