Microelectromechanical Systems (MEMS) Interrupter for Safe and Arm Devices

This thesis addresses the development of a new micro-scale interrupter mechanism for a safe and arm device used in modern weapon systems. The interrupter mechanism often consists of a physical barrier that prevents an initial source of energy, in an explosive train, from being transferred to subsequent charges. In general, when the physical barrier is removed, the weapon is considered armed, and the charge is allowed to propagate. Several issues facing current safe and arm devices systems are the shrinking industrial base for manufacturing these devices and the desire for modern safe and arm devices to be compatible with next generation weapon systems that are generally decreasing in size and increasing in complexity. The solution proposed here is to design, fabricate, and test a conceptual interrupter mechanism using Microelectromechanical Systems (MEMS) components. These components have inherent benefits over current devices, such as smaller feature sizes and lower part counts, which have the capability to improve performance and reliability. After an extensive review of existing micro-scale safe and arm devices currently being developed, a preliminary design was fabricated in a polysilicon surface micromachining process. The operating principle of this conceptual interrupter mechanism is to have MEMS actuators slide four overlapping plates away from each other to create an aperture, thus providing an unimpeded path for an initiating energy source to propagate. Operation of the fabricated MEMS interrupter mechanism was successfully demonstrated with an approximate aperture area of 1024 μm2 being created

Design, Fabrication, and Testing of Time Delay Micromechanisms for Fuzing Systems

Micromechanical sequential-leaf time delay mechanisms based on SOI/DRIE technology have been designed, fabricated, and characterized. The devices were designed as elements of a larger fuzing system for rifled munitions, in which a passive timing mechanism triggers at a predetermined rotational speed, followed by a desired delay time before the next element of the munition fuzing train is activated. Analytical models for the micromechanical timing mechanisms have been developed and a variety of designs was simulated from the linear and nonlinear models, and using dynamics simulation software. Fabricated mechanism arrays designed to initiate switching at centripetal accelerations from 44 to 263 g were characterized using a high-speed camera, with delay times of between 0.67 and 0.95 ms achieved for single elements within the arrays. Measured delay times and switching accelerations follow predicted trends based on analytical and numerical models. Runaway escapement mechanism was coupled with the sequential-leaf time delay mechanisms to increase the delay time of each mechanism element. Mechanism switching at 2,000 g have been designed and simulated. The predicted delay time of each mechanism element was approximately doubled with the coupled runaway escapement mechanism. Two types of locking mechanisms were developed to increase reliability of operation of the sequential-leaf time delay mechanisms. The fish-bone type locking mechanism had been successfully demonstrated. A generic testing method for rotational dynamics that could image small displacement of object with high-speed off axis rotation was developed, which demonstrated for the first time of real time monitoring for rotational time delay mechanism. Image processing technology was used to improve image quality of high-speed images and extend the capability of high-speed camera to adapt to high rotation speed tests and to assist in post image analyses

낮은 임계 가속도를 가지는 실리콘 기반 MEMS 가속도 스위치에 관한 연구

학위논문 (박사)-- 서울대학교 대학원 공과대학 전기·컴퓨터공학부, 2017. 8. 김용권.Abstract In this paper, MEMS acceleration switch with low threshold acceleration below 10 g and fine environmental characteristics are developed. Limits of the previously reported low-g MEMS switches were addressed in terms of environmental test issues and the solutions for them were suggested and integrated in the proposed low-g MEMS acceleration switch. Fabrication process consists of one silicon-on-insulator substrate and two glass substrates for base and package, respectively. Single-crystalline silicon was chosen as the structural material for high thermal stability and stress-free structure. After the fabrication, height profiles of the free-hanging proof masses were measured to show that the fabricated switches does not suffer from stress problems. The size of single switch was measured as 2150 x 4240 x 1180 µm3 and the average proof mass, initial gap, and the spring constant was 307.38 µg, 6.39 µm, and 3.29 N/m, respectively. The calculated threshold acceleration thus was 6.98 g. In the electrostatic operation test, the response time of the switch was measured to be shorter than 1.2 ms and the minimum contact resistance was 8.5 Ω at the contact force of 284 µN. Life cycle test was carried out to show that the developed switch could operate more than 10,000 cycles without failure. Rotation-table experiment was carried out in sequence to reveal that the switch operates at 6.61 g. The error analysis was carried out in the consideration of the off-axis force generated during the rotation-table experiment. From the experimental values, the off-axis force was calculated as 2.091 μN and the resulting reduction in the initial switching gap was simulated as 0.236 μm. The reduced threshold acceleration thus was estimated to be 6.512 g, which agrees well with the measured threshold acceleration value of 6.61 g. Rotation-table test using another switch was conducted to model the relation between the off-axis force and the operating acceleration of the developed switch. Least squares method was used in the analysis and the original threshold acceleration (a_th) of the switch was calculated as 6.16325 g. The error rate (ε) due to the off-axis force was calculated as -0.22693 g/µN. The modeled operating acceleration of the switch in terms of the off-axis force matched well with the measurements, showing the maximum error less than 1.6%. Heating, sealing, high-g, and impact tests were conducted in sequence to validate the environmental characteristics of the switch. Test condition of 80 °C for 6 hours were adopted for heating test and the tested switch operated more than 200 cycles normally after the test. For sealing test, gross leak test using penetrant dye (Rhodamine B) and fine leak test using tracer gas (helium) were conducted sequentially. 10 samples were put into both of the tests. In the gross leak test, no signs of dye penetration were observed after pressurizing the samples in the dye solution. The tested switches were then put into the fine leak test. In the fine leak test, helium leak rates were measured and all of the tested samples showed leak rate lower than 5.8x10-8 atm cc/s He, which is the reject limit provided by MIL-STD-883E. High-g test and drop impact test were also performed to validate the effectiveness of the displacement-restricting structure. As a result of the high-g test, the developed switch was able to operate without breaking after experiencing the acceleration of 300 g in the ±x ̂, ±y ̂, and ±z ̂ axes. In addition, the drop impact test has proved that the developed switch can withstand an impact as high as 1000 g. The MEMS acceleration switch developed throughout this study is the first to attain low threshold and good environmental characteristics at the same time. Therefore, the author believes that the switch developed in this study is the most suitable one for safety arm unit application among the low-g switches developed so far.1. Introduction 1 1.1. Sensing of acceleration 1 1.2. Safety arm unit and MEMS acceleration switches 8 1.3. Literature review 14 1.4. Motivation and purpose 19 1.5. Contribution 20 1.6. Composition of thesis 22 2. Theory and design of low-g MEMS acceleration switch 23 2.1. Basic theories on acceleration switch 23 2.1.1 Static threshold acceleration 23 2.1.2 Determining the initial gap 25 2.1.3 Serpentine spring 27 2.1.4 Parallel plate damper 31 2.2. Model description 34 2.2.1 Base glass substrate 36 2.2.2 SOI substrate 36 2.2.3 Packaging glass substrate 37 2.3. FEM simulation 38 2.3.1 Force, displacement, stress simulation 38 2.3.2 Modal analysis Resonant frequency 40 2.4. MATLAB code for MEMS switch 45 3. Fabrication of low-g MEMS acceleration switch 63 3.1. Overall fabrication process 63 3.2. Base glass substrate 65 3.3. SOI substrate 69 3.4. Bonded susbtrate & packaging 72 3.5. Fabrication results 79 4. Characterization of low-g MEMS acceleration switch 84 4.1. DC operation test & lifecycle test 84 4.2. Rotation-table experiments 93 4.3. Effect of the off-axis force on the operating acceleration 101 4.4. Heating test 111 4.5. Sealing test 112 4.6. High-g test & drop impact test 118 5. Conclusion 125 References 128 Abstract (Korean) 136Docto

MEMS Accelerometers

Micro-electro-mechanical system (MEMS) devices are widely used for inertia, pressure, and ultrasound sensing applications. Research on integrated MEMS technology has undergone extensive development driven by the requirements of a compact footprint, low cost, and increased functionality. Accelerometers are among the most widely used sensors implemented in MEMS technology. MEMS accelerometers are showing a growing presence in almost all industries ranging from automotive to medical. A traditional MEMS accelerometer employs a proof mass suspended to springs, which displaces in response to an external acceleration. A single proof mass can be used for one- or multi-axis sensing. A variety of transduction mechanisms have been used to detect the displacement. They include capacitive, piezoelectric, thermal, tunneling, and optical mechanisms. Capacitive accelerometers are widely used due to their DC measurement interface, thermal stability, reliability, and low cost. However, they are sensitive to electromagnetic field interferences and have poor performance for high-end applications (e.g., precise attitude control for the satellite). Over the past three decades, steady progress has been made in the area of optical accelerometers for high-performance and high-sensitivity applications but several challenges are still to be tackled by researchers and engineers to fully realize opto-mechanical accelerometers, such as chip-scale integration, scaling, low bandwidth, etc

Track detection in railway sidings based on MEMS gyroscope sensors

The paper presents a two-step technique for real-time track detection in single-track railway sidings using low-cost MEMS gyroscopes. The objective is to reliably know the path the train has taken in a switch, diverted or main road, immediately after the train head leaves the switch. The signal delivered by the gyroscope is first processed by an adaptive low-pass filter that rejects noise and converts the temporal turn rate data in degree/second units into spatial turn rate data in degree/meter. The conversion is based on the travelled distance taken from odometer data. The filter is implemented to achieve a speed-dependent cut-off frequency to maximize the signal-to-noise ratio. Although direct comparison of the filtered turn rate signal with a predetermined threshold is possible, the paper shows that better detection performance can be achieved by processing the turn rate signal with a filter matched to the rail switch curvature parameters. Implementation aspects of the track detector have been optimized for real-time operation. The detector has been tested with both simulated data and real data acquired in railway campaigns.Peer ReviewedPostprint (published version

Integrated through -wafer optical monitoring of MEMS for closed -loop control

Current trends in many microelectronic systems show an increased use of microelectromechanical systems (MEMS) to perform a variety of tasks. The increased market for MEMS has led to microsystem technologies being employed in physically demanding environments and safety critical applications. This creates the need for higher degrees of certainty in MEMS operation, especially in systems that contain drive components operating under time varying load conditions. Situations such as these give rise to the need for detailed knowledge of the operational states of MEMS over the lifetime of the device, as well as device fault detection. Accurately obtaining this information by a means decoupled from the system shows the potential to further enable both complex and simple MEMS, and allows for the application of closed-loop control. Preliminary through-wafer optical monitoring research efforts have shown that through-wafer optical probing is suitable for characterizing and measuring the behavior of lateral harmonic oscillators.;This presentation will discuss research undertaken to establish integrated optical monitoring (IOM) for closed-loop control. Design of the optical microprobe setup, as well as device geometry, were completed to achieve a through-wafer optical signal with increased positional resolution and mechanical stability. Successful linear closed-loop control results achieved using the redesigned probe setup and devices will be presented. Increased displacement information in the optical output waveform is needed for the successful application of more robust, nonlinear control routines. Theoretical optical output field intensity studies are presented and compared with experimental output waveforms, showing a positional resolution of 2 pim using grating structures. Initial binary Fresnel diffractive optical microelement design layout, fabrication parameters, and testing results will be given as well for implementation of a fully integrated optical monitoring system

Proof-of-concept of a single-point Time-of-Flight LiDAR system and guidelines towards integrated high-accuracy timing, advanced polarization sensing and scanning with a MEMS micromirror

Dissertação de mestrado integrado em Engenharia Física (área de especialização em Dispositivos, Microssistemas e Nanotecnologias)The core focus of the work reported herein is the fulfillment of a functional Light Detection and Ranging (LiDAR) sensor to validate the direct Time-of-Flight (ToF) ranging concept and the acquisition of critical knowledge regarding pivotal aspects jeopardizing the sensor’s performance, for forthcoming improvements aiming a realistic sensor targeted towards automotive applications. Hereupon, the ToF LiDAR system is implemented through an architecture encompassing both optical and electronical functions and is subsequently characterized under a sequence of test procedures usually applied in benchmarking of LiDAR sensors. The design employs a hybrid edge-emitting laser diode (pulsed at 6kHz, 46ns temporal FWHM, 7ns rise-time; 919nm wavelength with 5nm FWHM), a PIN photodiode to detect the back-reflected radiation, a transamplification stage and two Time-to-Digital Converters (TDCs), with leading-edge discrimination electronics to mark the transit time between emission and detection events. Furthermore, a flexible modular design is adopted using two separate Printed Circuit Boards (PCBs), comprising the transmitter (TX) and the receiver (RX), i.e. detection and signal processing. The overall output beam divergence is 0.4º×1º and an optical peak power of 60W (87% overall throughput) is realized. The sensor is tested indoors from 0.56 to 4.42 meters, and the distance is directly estimated from the pulses transit time. The precision within these working distances ranges from 4cm to 7cm, reflected in a Signal-to-Noise Ratio (SNR) between 12dB and 18dB. The design requires a calibration procedure to correct systematic errors in the range measurements, induced by two sources: the timing offset due to architecture-inherent differences in the optoelectronic paths and a supplementary bias resulting from the design, which renders an intensity dependence and is denoted time-walk. The calibrated system achieves a mean accuracy of 1cm. Two distinct target materials are used for characterization and performance evaluation: a metallic automotive paint and a diffuse material. This selection is representative of two extremes of actual LiDAR applications. The optical and electronic characterization is thoroughly detailed, including the recognition of a good agreement between empirical observations and simulations in ZEMAX, for optical design, and in a SPICE software, for the electrical subsystem. The foremost meaningful limitation of the implemented design is identified as an outcome of the leading-edge discrimination. A proposal for a Constant Fraction Discriminator addressing sub-millimetric accuracy is provided to replace the previous signal processing element. This modification is mandatory to virtually eliminate the aforementioned systematic bias in range sensing due to the intensity dependency. A further crucial addition is a scanning mechanism to supply the required Field-of-View (FOV) for automotive usage. The opto-electromechanical guidelines to interface a MEMS micromirror scanner, achieving a 46º×17º FOV, with the LiDAR sensor are furnished. Ultimately, a proof-of-principle to the use of polarization in material classification for advanced processing is carried out, aiming to complement the ToF measurements. The original design is modified to include a variable wave retarder, allowing the simultaneous detection of orthogonal linear polarization states using a single detector. The material classification with polarization sensing is tested with the previously referred materials culminating in an 87% and 11% degree of linear polarization retention from the metallic paint and the diffuse material, respectively, computed by Stokes parameters calculus. The procedure was independently validated under the same conditions with a micro-polarizer camera (92% and 13% polarization retention).O intuito primordial do trabalho reportado no presente documento é o desenvolvimento de um sensor LiDAR funcional, que permita validar o conceito de medição direta do tempo de voo de pulsos óticos para a estimativa de distância, e a aquisição de conhecimento crítico respeitante a aspetos fundamentais que prejudicam a performance do sensor, ambicionando melhorias futuras para um sensor endereçado para aplicações automóveis. Destarte, o sistema LiDAR é implementado através de uma arquitetura que engloba tanto funções óticas como eletrónicas, sendo posteriormente caracterizado através de uma sequência de testes experimentais comumente aplicáveis em benchmarking de sensores LiDAR. O design tira partido de um díodo de laser híbrido (pulsado a 6kHz, largura temporal de 46ns; comprimento de onda de pico de 919nm e largura espetral de 5nm), um fotodíodo PIN para detetar a radiação refletida, um andar de transamplificação e dois conversores tempo-digital, com discriminação temporal com threshold constante para marcar o tempo de trânsito entre emissão e receção. Ademais, um design modular flexível é adotado através de duas PCBs independentes, compondo o transmissor e o recetor (deteção e processamento de sinal). A divergência global do feixe emitido para o ambiente circundante é 0.4º×1º, apresentando uma potência ótica de pico de 60W (eficiência de 87% na transmissão). O sensor é testado em ambiente fechado, entre 0.56 e 4.42 metros. A precisão dentro das distâncias de trabalho varia entre 4cm e 7cm, o que se reflete numa razão sinal-ruído entre 12dB e 18dB. O design requer calibração para corrigir erros sistemáticos nas distâncias adquiridas devido a duas fontes: o desvio no ToF devido a diferenças nos percursos optoeletrónicos, inerentes à arquitetura, e uma dependência adicional da intensidade do sinal refletido, induzida pela técnica de discriminação implementada e denotada time-walk. A exatidão do sistema pós-calibração perfaz um valor médio de 1cm. Dois alvos distintos são utilizados durante a fase de caraterização e avaliação performativa: uma tinta metálica aplicada em revestimentos de automóveis e um material difusor. Esta seleção é representativa de dois cenários extremos em aplicações reais do LiDAR. A caraterização dos subsistemas ótico e eletrónico é minuciosamente detalhada, incluindo a constatação de uma boa concordância entre observações empíricas e simulações óticas em ZEMAX e elétricas num software SPICE. O principal elemento limitante do design implementado é identificado como sendo a técnica de discriminação adotada. Por conseguinte, é proposta a substituição do anterior bloco por uma técnica de discriminação a uma fração constante do pulso de retorno, com exatidões da ordem sub-milimétrica. Esta modificação é imperativa para eliminar o offset sistemático nas medidas de distância, decorrente da dependência da intensidade do sinal. Uma outra inclusão de extrema relevância é um mecanismo de varrimento que assegura o cumprimento dos requisitos de campo de visão para aplicações automóveis. As diretrizes para a integração de um micro-espelho no sensor concebido são providenciadas, permitindo atingir um campo de visão de 46º×17º. Conclusivamente, é feita uma prova de princípio para a utilização da polarização como complemento das medições do tempo de voo, de modo a suportar a classificação de materiais em processamento avançado. A arquitetura original é modificada para incluir uma lâmina de atraso variável, permitindo a deteção de estados de polarização ortogonais com um único fotodetetor. A classificação de materiais através da aferição do estado de polarização da luz refletida é testada para os materiais supramencionados, culminando numa retenção de polarização de 87% (tinta metálica) e 11% (difusor), calculados através dos parâmetros de Stokes. O procedimento é independentemente validado com uma câmara polarimétrica nas mesmas condições (retenção de 92% e 13%)

Through-wafer interrogation of MEMS device motion

Microelectromechanical systems (MEMS) have been the focus of many research groups because of their wide variety of uses in sensing and actuation applications. A fundamental barrier facing designers of next generation MEMS is the inability to access accurate, real-time microstructure positional information to determine if the device is performing as expected. Previously explored optical and electrical methods of MEMS device monitoring are often only suitable for research environments, or are unable to produce clear and meaningful characterization of device motion. The most desirable MEMS monitoring method would be one that could be implemented at the device level, which would allow the monitoring system to be fabricated along with the device itself. This research explores a through-wafer method of optically monitoring and characterizing the motion of a lateral comb resonator fabricated using the Multi-User MEMS Process Service (MUMPS). Positional monitoring results obtained from a 1.3 mum wavelength through-wafer optical probe are presented, as well as a method of device level implementation of the monitoring system

Geometric Effects on the Wear of Microfabricated Silicon Journal Bearings

This dissertation presents an investigation of geometric effects on the wear of large aspect ratio silicon journal microbearings. The consideration of geometric conformality of rotor and hub as a critical design parameter manifests from the inherent properties of deep reactive ion etching as part of the current MEMS fabrication process employed in this dissertation. The investigation is conducted in two phases, each characterized by novel microbearing designs, fabrication processes, experimental test methodologies, and characterization techniques. The intent of Phase 1 is to focus on the effects of conformality of wear, while the intent of Phase 2 is to focus on the effects of clearance on wear. Manual assembly of rotors and hubs allows a broader range of custom bearing clearances than would otherwise be available from lithographic, pattern transfer, and etching capabilities of current in situ MEMS fabrication technologies. Novel wear indicators, intended to facilitate the rapid quantitative and qualitative determination of wear, are incorporated in the Phase 2 rotor designs. Two particular enabling features of the novel fabrication processes, namely the sprue and float etching methods, are developed in this dissertation. The sprues, patterned using the DRIE mask, hold the rotors in place during the KOH etching process. The float etching technique entails floating the device wafer on top of the KOH etchant bath. The results obtained from using the first apparatus indicate that microbearing performance, as measured by rotor rotational speed and rotor cumulative wear, is strongly dependent on conformality. The results obtained using the second apparatus indicate that microbearing rotor rotational velocity is strongly dependent on radial clearance parameter C0. A dynamic impact model of the bearing system based on classical impulse-momentum relations is formulated in order to assess the effect of clearance on rotor rotational speed. A coefficient of restitution is obtained for silicon-on-silicon surfaces over the range of kinematically allowable radial clearance specifications