Implementation of the Proposed Reliability Assurance Strategy for an InGaAsP/InP, Planar Mesa, Buried Heterostructure Laser Operating at 1.3 μm for Use in a Submarine Cable

Abstract

We discuss the implementation of a strategy designed to provide laser-lightemitting reliability assurance for 1.3-μνα InGaAsP/lnP lasers of the planar mesa, buried heterostructure type for use in a submarine cable application. The testing regimes include initial characterization (cosmetic and light-current curve inspection), passive aging (elevated temperatures [85 to 175°C] without bias, with and without humidity [<85-percent relative humidity]), overstress active aging (high temperatures [150°C], high currents [250 mAdc]), and longterm rate-monitoring active aging (elevated temperature [60°C] burn-in [3 mW/facet]). Overstress testing is designed to compel a timely (~10 2 -hour) identification of premature failures, due to modes of degradation other than the long-term ultimately controlling wear-out mode, and to stabilize transient modes. To identify premature failures of the wear-out type, survivors of overstressing are subjected to rate monitoring in which wear-out degradation rates, established in a reasonable time (~10 3 hours), may be sorted. The principal results of the important overstress aging were the detection of an initially occurring saturable degradation mode, present to some extent in most lasers, and a regimen to force its rapid stabilization, so that it would not obscure determination of the activation energy of the wear-out mode. With a credibly determined value for the latter, it was deterministically inferred from * Authors are employees of AT&T Bell Laboratories.

Methodology of Accelerated Aging

“…Finally, the projection method is sometimes improved if the com ponents are stabilized*· 6 in advance of the monitoring period on which the projection is based. The main idea of stabilization is to drive to saturation or to anneal any initial transients in the degradation rate.…”

“…[22] over a useful temperature range and the approxi mate invariance of T 0 during aging have been reported for certain types of lasers. 6,12 ) Without specifying the time dependence of the isothermal aging law, we define a possibly-time-dependent b a -by the requirement that isothermal aging along the solid-line path 1-5 in Fig. 4 causes ii = i(t = 0, T a ·) to evolve into 4, i.e., b a -4 is defined as the isothermal increase in 4,…”

“…Specific procedures, or combina tions of procedures, are known by such names as inspecting, perform ance evaluating, burning-in, accelerated burning-in, gettering, outgassing, tailored accelerated screening, 2 high-stress screening, 2,3 overstressing, purging, 4 " 6 stabilization, 4,6 etc., and the reader is referred to the literature for their explicit descriptions. In the present section we simply outline a framework for characterizing such reliability proce dures.…”

“…When the degradation is reversible (e.g., can be annealed out) the measurement of m is conceptually straightforward. Otherwise, m can be measured on a population basis by comparing the degradation times or rates for two statistically equivalent populations aged at two tem peratures (isothermal aging) 2 · 3 ' 6 ·™ or, on an individual-device basis, by partially aging a single device alternately at two stress levels (step stressing) 3,6 · 12,13 · 1 * and then scaling the time intervals at T a by that m that yields a smooth I(t) curve, all measurements of I being made at T r . (Any transients associated with the temperature change are often small enough to be confidently removed in the analysis with short backward extrapolations of the post-transient data.…”

“…Another truncation strategy, which is incorporated, for example, in the purge [4][5][6] and the tailored-accelerating-screen 2 procedures, is prem ised on the following physical model: All components eventually fail because all possess a common wear-out mechanism. In addition, certain flawed components are also afflicted with a second failure mechanism having a shorter life under normal operating conditions.…”