Numerical investigation of an impact of a top gold metallization on output power of a p-up III-N-based blue-violet edge-emitting laser diode

The effect of modifications in epi-side (top) gold metallization on a thermal performance and on power roll-over of blue-vio- let III-N-based p-up edge-emitting ridge-waveguide laser diode (RW EEL) was explored in this paper. The calculations were carried out using a two-dimensional self-consistent electrical-thermal model combined with a simplified optical model tuned to a RW EEL fabricated in the Institute of High Pressure Physics (Unipress). Our results suggest that with proper modifica- tions in the III-N-based RW EEL, excluding modifications in its inner structure, it is possible to considerably improve the thermal performance and, thus, increase the maximal output power.

Low-cost lithographically patterned source/drain bottom contacts for high mobility p-type organic thin film transistors

ABSTRACTShort channel organic thin film transistors in bottom-gate, bottom contact configuration use typically gold metallization for the source and drain contacts because this metal can easily be cleaned from photoresist residuals by oxygen plasma or ultraviolet-ozone and allows also surface modification by self-assembled monolayers (e.g. thiols). Alternative low-cost bottom contact metallization for high performance short-channel organic thin film transistors are scarce because of the incompatibility of the bottom contact material with the cleaning step. In this work a new process flow, involving a temporary thin aluminum protection layer, is presented. Short channel (3.4 μm) pentacene transistors with lithographical defined and thiol modified silver source/drain bottom contacts (25 nm thick, on a 2 nm titanium adhesion layer) prepared according to this process achieved a saturation mobility of 0.316 cm2/(V.s), and this at a metal cost below 1% of the standard 30 nm thick gold metallization.

Mechanical Robustness of Solder Connections to Thick Film Gold

Thick film gold metallization is required for many high reliability circuits, especially those subjected to operation in high temperature or high humidity environments. Traditionally, wire bonded bare die are used on these circuits, but there is a trend to replace them with BGA packaged devices. State-of-the-art, chip scale packages increase circuit volume by less than 20 percent, while their use greatly simplifies testing and repair, as compared to wire bonded die. The use of small, high density I/O pad arrays for attachment of BGA packages, necessitates very careful control of the solder reflow process to avoid excessive leaching of the gold into the solder. Also, unlike passive chip components and leaded devices, the solder filet associated with a solder ball attachment does not distribute mechanical loads over an extended area. Consequently, the stresses imposed on fine pitch, BGA pads are much higher than those imposed by other components. During aging, the gold metallization is converted to gold-tin intermetallic as inter-diffusion proceeds. This further reduces the mechanical integrity of the solder connection. This manifests itself in the observation that when BGA solder balls are subjected to accelerated aging followed by shear testing, the entire solder pad lifts off of the substrate, rather than failing in the solder joint. What we have done is construct a diffusion based model to estimate the conversion of a thick film gold metallization pad to intermetallic and coupled this result with a finite element analysis to examine the effect of pad size and solder composition on the propensity of a pad to lift off the substrate, when subjected to mechanical or thermal induced loading. We are designing experiments to compare the predictions of our model to experimental results obtained from shearing solder balls, of different compositions and sizes, attached to substrates metalized with several different solderable, thick film gold materials.

MEMS Device Sealing in a High Vacuum Atmosphere Achieving Long Term Reliable Vacuum Levels

Microeletromechanical Systems (MEMS) require encapsulation of delicate microelements in a controlled atmosphere or vacuum environment. In order to achieve proper device operation and protection from harsh environments, these packages must be hermetically sealed and the internal atmosphere must be maintained to prevent degradation of the device over it's lifetime. Controlled atmospheres and vacuum levels can change over time due to improper consideration of material and their outgassing characteristics. Packaging of MEMS has been and continues to be a major challenge unless all of the materials comprising of a sealed package are evaluated at the initial design phase. This paper will address the issues related to a ceramic package with a gold metallization seal ring, the importance of using low outgassing sensor attach materials, incorporating a getter material to be sealed in the package cavity, and the proper handling of the hermetic lid. In order to achieve the best and highest entrapped vacuum in the package, materials must be prepared before processing. This will involve proper vacuum baking and activating the getter film prior to sealing the MEMS device. By controlling the vacuum levels with aggressive bake outs, fully activating the getter, addressing all material out gassing rates, and optimizing the high vacuum sealing process profile a MEMS device with a controlled vacuum level can be obtained.