Kenneth A. Peterson

MEMS Reliability: Infrastructure, Test Structures, Experiments, and Failure Modes

The burgeoning new technology of Micro-Electro-Mechanical Systems (MEMS) shows great promise in the weapons arena. We can now conceive of micro-gyros, micro-surety systems, and micro-navigators that are extremely small and inexpensive. Do we want to use this new technology in critical applications such as nuclear weapons? This question drove us to understand the reliability and failure mechanisms of silicon surface-micromachined MEMS. Development of a testing infrastructure was a crucial step to perform reliability experiments on MEMS devices and will be reported here. In addition, reliability test structures have been designed and characterized. Many experiments were performed to investigate failure modes and specifically those in different environments (humidity, temperature, shock, vibration, and storage). A predictive reliability model for wear of rubbing surfaces in microengines was developed. The root causes of failure for operating and non-operating MEMS are discussed. The major failure mechanism for operating MEMS was wear of the polysilicon rubbing surfaces. Reliability design rules for future MEMS devices are established.

First Reliability Test of a Surface Micromachined Microengine Using SHiMMeR

The first-ever reliability stress test on surface micromachined microengines developed at Sandia National Laboratories has been completed. We stressed 41 microengines at 36,000 RPM and inspected the functionality at 60 RPM. We have observed an infant mortality region, a region of low failure rate, and no signs of wearout in the data. The reliability data are presented and interpreted using standard reliability methods. Failure analysis results on the stressed microengines are presented. In our effort to study the reliability of MEMS, we need to observe the failures of large numbers of parts to determine the failure modes. To facilitate testing of large numbers of micromachines, we designed and built an automated system that has the capability to simultaneously test 256 packaged micromachines. The Sandia high volume measurement of micromachine reliability system has computer controlled positioning and the capability to inspect moving parts. The development of this parallel testing system is discussed in detail.

Failure modes in surface micromachined microelectromechanical actuators

In order for the rapidly emerging field of microelectromechanical systems (MEMS) to meet its extraordinary expectations with regard to commercial impact, issues pertaining to failure must be understood. We identify failure modes common to a broad range of MEMS actuators, including adhesion (stiction) and friction-induced failures caused by improper operational methods, mechanical instabilities, and electrical instabilities. Demonstrated methods to mitigate these failure modes include implementation of optimized designs, model-based operational methods, and chemical surface treatments.

Effects of focused ion beam irradiation on MOS transistors

The effects of irradiation from a focused ion beam (FIB) system on MOS transistors are reported systematically for the first time. Three MOS transistor technologies, with 0.5, 1, and 3 /spl mu/m minimum feature sizes and with gate oxide thicknesses ranging from 11 to 50 nm, were analyzed. Significant shifts in transistor parameters (such as threshold voltage, transconductance, and mobility) were observed following irradiation with a 30 keV Ga/sup +/ focused ion beam with ion doses varying by over 5 orders of magnitude. The apparent damage mechanism (which involved the creation of interface traps, oxide trapped charge, or both) and extent of damage were different for each of the three technologies investigated.

Failure analysis of surface-micromachined microengines

Microelectronic failure analysis (FA) has been an integral part of the development of state-of-the-art integrated circuits. FA of MicroElectroMechanical Systems (MEMS) is moving from its infancy to assume an important role in the successful design, fabrication, performance and reliability analysis for this new technology. In previous work, we focused on the application of several techniques developed for integrated circuit analysis to an earlier version of a surface micromachined microengine fabricated at Sandia. Recently, we have identified important new failure modes in binary counters that incorporate a newer design of the microengine, using a subset of integrated circuit failure analysis techniques including optical microscopy, focused ion beam (FIB) techniques, atomic force microscopy (AFM), and scanning electron microscopy (SEM). The primary failure mode we have identified is directly related to visible wear on bearing surfaces. In this paper, we describe in detail the characteristics of the failure modes in binary counters. We also compare the failure characteristics with those of an earlier version of the microengine.

Low Temperature Cofired Ceramic Microfluidic Microsystems for High Temperature and High Pressure Applications

As an alternative material to glass, silicon, and plastics, Low Temperature Cofired Ceramic (LTCC) substrate technology is becoming increasingly important for enabling microfluidic microsystems and devices for integrated chemical and biological analysis. LTCCs simple fabrication method and unique ability to withstand high temperatures and high pressures make it well-suited for applications not possible with traditional materials. As part of Sandias initiative to develop an automated sample preparation system for the μChemlab™ bioagent detector, an integrated microfluidic lyser using LTCC technology has been fabricated, which enables the use of aqueous buffers at high temperatures without boiling by using a pressurized system. Thermal lysing of bacterial spores in a flow-through microfluidic device at temperatures as high as 220°C and pressures up to 10.3 MPa (1,500 psi) represents a new method for solubilizing spore proteins for identification and analysis, eliminating the reliance on harsh chemical red...

Development of LTCC Smart Channels for Integrated Chemical, Temperature, and Flow Sensing

This paper describes the development of “smart” channels that can be used simultaneously as a fluid channel and as an integrated chemical, temperature, and flow sensor. The uniqueness of this device lies in the fabrication and processing of low-temperature co-fired ceramic (LTCC) materials that act as the common substrate for both the sensors and the channel itself. Devices developed in this study have employed rolled LTCC tubes, but grooves or other channel shapes can be fabricated depending on the application requirements. The chemical transducer is fabricated by depositing a conductive polymer “ink” across a pair of electrodes that acts as a chemical resistor (chemiresistor) within the rolled LTCC tube. Volatile organic compounds passing through the tube are absorbed into the polymers, causing the polymers to reversibly swell and change in electrical resistance. The change in resistance is calibrated to the chemical concentration. Multiple chemiresistors have been integrated into a single smart channel...

OBIC analysis of stressed, thermally-isolated polysilicon resistors

High gain Optical Beam Induced Current (OBIC) imaging has been used for the first time to examine the internal structural effects of electrical stress on thermally-isolated polysilicon resistors. The resistors are examined over a wide range of current densities, producing Joule heating up to /spl sim/1200/spl deg/C. Throughout this current density range, the OBIC images indicate a clustering of dopant under dc stress and a more uniform distribution under ac conditions. The OBIC images also reveal areas that are precursors to catastrophic resistor failure. In addition to OBIC imaging, conventional electrical measurements were performed, examining the polysilicon resistance degradation and time-to-failure as a function of electrical stress. The electrical measurements show a monotonic increase in polysilicon resistor lifetime with frequency (up to 2 kHz) when subjected to a bipolar ac stress. The enhanced lifetime was observed even under high temperature (from Joule heating) stress conditions previously reported to be electromigration-free. The dopant redistribution indicated by the OBIC images is consistent with an electromigration stress experienced by the polysilicon resistors. The implications for thermally-isolated polysilicon resistor reliability are examined briefly.

50-W LTCC Transmitter Utilizing 28-V GaAs With Integrated High-Speed Pulse Modulation

This letter presents an S-band 50-W low-temperature cofired ceramic (LTCC) transmitter module. The module is based on a gallium arsenide (GaAs) chipset that operates over the 2-3 GHz range and includes a 28-V single-chip power amplifier with integrated high-speed drain modulator. The transmitter has rise/fall times < 7 nsec, linear frequency tuning, and excellent thermal performance.

Electrokinetically Pumped Liquid Propellant Microthrusters for Orbital Station Keeping

For most orbital maneuvers, small satellites in the sub-10 kg range require thrusters capable of spanning the micro-Newton to milli-Newton force range. At this scale, electrokinetic (EK) pumping offers precise metering of monergolic or hypergolic liquid propellants under purely electrical control at pressures and flow rates well-suited to microthruster applications. We have demonstrated direct and indirect EK pumping for delivery of anhydrous hydrazine and hydrogen peroxide monopropellants, respectively, into capillary-based microthrusters with integrated in-line catalyst beds. Catalytic decomposition generates gases which accelerate through a plasma-formed converging-diverging nozzle, producing thrust. Specific impulses up to 190 s have been shown for hydrazine in non-optimized nozzles.