Microelectromechanical Systems Micro Research Articles

Wafer-Level Manufacturing of MEMS H2 Sensing Chips Based on Pd Nanoparticles Modified SnO2 Film Patterns.

In this manuscript, a simple method combining atomic layer deposition and magnetron sputtering is developed to fabricate high-performance Pd/SnO2 film patterns applied for micro-electro-mechanical systems (MEMS) H2 sensing chips. SnO2 film is first accurately deposited in the central areas of MEMS micro hotplate arrays by a mask-assistant method, leading the patterns with wafer-level high consistency in thickness. The grain size and density of Pd nanoparticles modified on the surface of the SnO2 film are further regulated to obtain an optimized sensing performance. The resulting MEMS H2 sensing chips show a wide detection range from 0.5 to 500ppm, high resolution, and good repeatability. Based on the experiments and density functional theory calculations, a sensing enhancement mechanism is also proposed: a certain amount of Pd nanoparticles modified on the SnO2 surface could bring stronger H2 adsorption followed by dissociation, diffusion, and reaction with surface adsorbed oxygen species. Obviously, the method provided here is quite simple and effective for the manufacturing of MEMS H2 sensing chips with high consistency and optimized performance, which may also find broad applications in other MEMS chip technologies.

Skate, overtravel, and contact force of tilted triangular cantilevers for microcantilever-based MEMS probe technologies

Microfabricated chip-edge microcantilevers are commonly used as surface probes, e.g. in near-field microscopy. Such probes normally function in the low-deflection regime, where their behaviour is very well understood and documented. In contrast, when microcantilevers are used for applications such as electrical testing probes, their deflection can be somewhat higher, taking them into the less well understood high-deflection regime of microelectromechanical systems (MEMS). Here, a scalable model for the relationship between the skate, overtravel, and resulting tip contact force in tilted triangular cantilevers—which are bending with high deflection and in contact with a flat surface—is presented. The model is tested experimentally using macroscopic triangular cantilevers—the experimental results agree well with the proposed model. The findings enable a practical solution for zero-skate in tapered MEMS probes to be suggested. It is hoped that the findings may be of use for probe engineers involved with on-wafer testing and designers of emerging MEMS micro cantilever-based probes.

Characteristics of Thermal Conductivity Hydrogen Sensor using MEMS Micro Heater Elements

Advanced hydrogen safety technology is essential for the realization of a hydrogen energy society. In this context, the role of hydrogen sensors are very important. Therefore, we have been developing a novel thermal conductivity gas sensor using a MEMS (Micro Electro Mechanical Systems) micro heater. This sensor is a low power, extremely robust device especially suited to detect hydrogen as hydrogen possesses the highest thermal conductivity of all known gases. The use of a MEMS heater to reduce the element size has resulted in a faster thermal response, resulting in a faster response to hydrogen compared to conventional sensors.

Validating the Critical Point of Spontaneous Parametric Downconversion for Over 600 Scanning MEMS Micromirrors on Wafer Level

Sensors and actuators based on resonant micro-electro-mechanical systems (MEMS), such as scanning micro mirrors, are well-established in automotive and consumer products. As the areas of application broaden, the requirements for the MEMS are increasing. Devices outside of the performance specifications have to be rejected which is costly due to the high processing times of MEMS technologies. In particular, nonlinear system behavior is often found to cause unexpected device failure or performance issues. Thus, accurate simulation or rather system models which account for nonlinear sensor dynamics can not only increase process yield, but more importantly, lead to a comprehensive understanding of the underlying physics and to improved MEMS design. We have studied [1] the possibility of a rather drastic device failure induced by nonlinearities on the example of a resonant scanning MEMS micro mirror. On the level of a few selected chips, we have carefully measured the complex nonlinear system behavior and modeled it by a nonlinear mode-coupling phenomenon known as spontaneous parametric down-conversion (SPDC). The most intriguing feature of SPDC is the sudden change from a rather linear to a nonlinear system behavior at the critical oscillation amplitude. However, the threshold only lies within the range of the mirror's operational amplitude, if certain frequency resonance conditions regarding the mechanical modes are met. Thus, the critical amplitude strongly depends on the frequency spectrum of the MEMS design which in turn is largely influenced by fabrication imperfections. We validate the dependence of the critical amplitude on the resonance condition by measuring it for over 600 micro mirrors on wafer-level. Our work does not only validate the theory of SPDC with measurements on such a large scale, but also demonstrates modeling strategies which are essential for MEMS product design.

Spontaneous Parametric Down-Conversion Induced by Non-Degenerate Three-Wave Mixing in a Scanning MEMS Micro Mirror

Scanning micro-mirror actuators are silicon-based oscillatory micro-electro-mechanical systems (MEMS). They enable laser distance measurements for automotive LIDAR applications as well as projection modules for the consumer market. For MEMS applications, the geometric structure is typically designed to serve a number of functional requirements. Most importantly, the mode spectrum contains a single high-Q mode, the drive mode, which per design is expected to yield the only resonantly excited geometric motion during operation. Yet here, we report on the observation of a resonant three-mode excitation via a process known as spontaneous parametric down-conversion. We show that this phenomenon, most extensively studied in the field of nonlinear optics, originates from three-wave coupling induced by geometric nonlinearities. In combination with further Duffing-type nonlinearities, the micro mirror displays a variety of nonlinear dynamical behaviour ranging from stationary state bifurcations to dynamical instabilities observable via amplitude modulations. We are able to explain and emulate all experimental observations using a single fundamental model. In particular, our analysis allows us to understand the conditions for the onset of three-wave down-conversion which if not accounted for in the design of the MEMS structure, can have drastic impact on its functionality even leading to fracture.

Research progress of micro-electro-mechanical systems micro gas chromatography columns

The gas chromatography (GC) column is a key component of the gas chromatographic system, which is mainly used for the separation of mixed gas components. Compared with the traditional GC column, the micro GC column based on micro-electro-mechanical systems (MEMS) technology has the advantages of lighter weight, smaller volume, lower power consumption, and faster analysis. Furthermore, it can be integrated into a portable instrument, such as a miniaturized GC. The research progress of micro GC columns based on MEMS technology is summarized in this paper. First, the theoretical basis of the MEMS micro GC column is stated. Then, the layout and inner structure of the MEMS micro GC column, the stationary-phase support, and the preparation of the stationary phase are summarized. Finally, trends in the development of MEMS micro GC columns are discussed.

Modeling and simulation of non-spiral coil for magnetic sensing applications

Microcoils are essential components in magnetic sensors made using Micro-electro-mechanical systems (MEMS) technology. Nonspiral microcoils have fabrication advantages over conventional spiral coils and can be effectively used in MEMS micro sensors for generation and detection of magnetic fields. In this work, an analytical model of peak flux density, sensitivity, and resolution for the nonspiral planar microcoil is reported for the first time. Self and mutual inductances of a non-spiral coil are used to calculate the flux density at the innermost turn of the coil. The model derived is compared with standard fabrication results, and it is found to be in good agreement with the experimental results.

Shock reliability enhancement for MEMS vibration energy harvesters with nonlinear air damping as a soft stopper

This paper presents a novel application of utilising nonlinear air damping as a soft mechanical stopper to increase the shock reliability for microelectromechanical systems (MEMS) vibration energy harvesters. The theoretical framework for nonlinear air damping is constructed for MEMS vibration energy harvesters operating in different air pressure levels, and characterisation experiments are conducted to establish the relationship between air pressure and nonlinear air damping coefficient for rectangular cantilever MEMS micro cantilevers with different proof masses. Design guidelines on choosing the optimal air pressure level for different MEMS vibration energy harvesters based on the trade-off between harvestable energy and the device robustness are presented, and random excitation experiments are performed to verify the robustness of MEMS vibration energy harvesters with nonlinear air damping as soft stoppers to limit the maximum deflection distance and increase the shock reliability of the device.

Locomotion Control of MEMS Micro Robot Using Pulse-Type Hardware Neural Networks

This paper presents the locomotion control of micro electro mechanical systems (MEMS) micro robot. MEMS micro robot demonstrates the locomotion control by the pulse-type hardware neural networks (P-HNN). P-HNN generates oscillatory patterns of electrical activity such as living organisms. The basic component of P-HNN is pulse-type hardware neuron model (P-HNM). P-HNM has same basic features of biological neurons such as threshold, refractory period, spatio-temporal summation characteristics and enables the generation of continuous action potentials. P-HNN was constructed by MOSFETs, can be integrated by CMOS technology. Same as the living organisms P-HNN realized the robot control without using software programs, or A/D converters. The size of micro robot fabricated by the MEMS technology was 4×4×3.5 [mm]. The frame of robot was made of silicon wafer, equipped with rotary type actuators, link mechanisms and 6 legs. MEMS micro robot emulated the locomotion method and the neural networks of the insect by rotary actuators, link mechanisms and P-HNN. As a result, we show that P-HNN can control the forward and backward locomotion of fabricated MEMS micro robot, and also switched the direction by inputting the external trigger pulse. The locomotion speed was 19.5 [mm/min] and the step width was 1.3 [mm].

On-demand multi-batch self-assembly of hybrid MEMS by patterning solders of different melting points

Self-assembly has been widely accepted as the next generation technology for integrating highly dense microelectromechanical systems (MEMS), in particular for complex and hybrid systems composed of sensing, actuating, optical, electronic, mechanical and fluidic components. In addition, some micro components may have the same material, size, shape and binding affinity, but different functions. Ideally, each micro component should bind and can only bind to a designated binding site with no recognition error even for similar sites. Due to the spontaneous nature of ‘self’-assembly, challenges remain in controlling this process. In this work, a relatively simple controllable, fluid-based self-assembly method has been demonstrated, which is able to integrate hybrid MEMS in a multi-batch-wise manner. The essence of this method is to pattern solders with different melting points to designated binding sites, and to activate them separately and sequentially, even individually if needed, with appropriate processing steps at adequate temperatures. Thus, self-assembly of MEMS micro components becomes programmable.

Abstract Additional informationNotes on contributors S Ahmad completed his master's degree from Allahabad University, Allahabad and PhD from BITS, Pilani in 65 and 70 respectively. This was followed by a brief teaching assignment at BITS, Pilani for about four years. He has been involved in R&D activities in the areas of microwave and millimeter wave semiconductor devices and technology, high power laser source packaging, Micro-electro-mechanical Systems (MEMS) and Micro Sensor Technology in the present organization for more than three decades. A clean room laboratory, equipped with modern device processing and characterization facilities, was set up by him to undertake sponsored projects in microwave and millimeter wave semiconductor device development. Later on, the laboratory was augmented with additional facilities for undertaking development work in the area of high power laser source packaging and MEMS micro sensors. Silicon Baritts, Impatts, high power CW laser sources, piezo-resistive pressure sensors, acoustic sensors, capacitive pressure sensors, RF switch, polysilicon load cells like products were developed in various programmes under his supervision. Device design activity started in his team using numerical solutions of charge carrier transport equations under practical boundary conditions. These efforts have resulted in about 60 publications in national and international journals and nine patents. Development of MEMS based chemical and biosensors, RF MEMS and inertial sensors are his current areas of interest. Dr Ahmad is presently coordinating the CSIR Network Program on MEMS and Micro Sensors in which nine laboratories are actively participating. Dr Ahmad is a Fellow of IETE and the Principal Hony. Editor of IETE Journal of Research. Dr S Ahmad is recipient of 19th RL Wadhwa Memorial Gold Medal Award from IETE. Dr Ahmad was Director of Central Electronics Engineering Research Institute, Pilani up to October 2003 and after that he is serving CSIR as Director Grade Scientist in Pilani.

MEMS-based miniature optical pickup

The technology challenges for miniature optical pickups include high-numerical-aperture objective lens design, servo actuator functions and performance, and component assembly tolerance. In this paper, a microelectromechanical systems (MEMS)-based miniature optical pickup is proposed for DVD and blue disk systems. A high-order diffractive objective lens with a continuous surface relief is designed. Focus, tilt, and tracking servos are implanted with MEMS micro actuators. Preliminary design and test results are presented.

Flow Characteristics in a Microchannel Fabricated on a Silicon Wafer

Recent developments in microfluidic devices based on microelectromechanical systems (MEMS) technique find many practical applications, which include electronic chip cooling devices, power MEMS devices, micro sensors, and bio-medical devices among others. For the design of such micro devices, flows characteristics inside a microchannel have to be clarified which exhibit somewhat different characteristics compared to conventional flows in a macrochannel. In the present study microchannels of various hydraulic diameters are fabricated on a silicon wafer to study the pressure drop characteristics. The effect of abrupt contraction and expansion is also studied. It is found from the results that the friction factor in a straight microchannel is about 15% higher than that in a conventional macrochannel, and the loss coefficients in abrupt expansion and contraction are about 10% higher than that obtained through conventional flow analysis.