Hybrid Microelectromechanical Systems Research Articles

Piezoelectrically and Capacitively Transduced Hybrid MEMS Resonator with Superior RF Performance and Enhanced Parasitic Mitigation by Low-Temperature Batch Fabrication

This study investigates a hybrid microelectromechanical system (MEMS) acoustic resonator through a hybrid approach to combine capacitive and piezoelectric transduction mechanisms, thus harnessing the advantages of both transducer technologies within a single device. By seamlessly integrating both piezoelectric and capacitive transducers, the newly designed hybrid resonators mitigate the limitations of capacitive and piezoelectric resonators. The unique hybrid configuration holds promise to significantly enhance overall device performance, particularly in terms of quality factor (Q-factor), insertion loss, and motional impedance. Moreover, the dual-transduction approach improves the signal-to-noise ratio and reduces feedthrough noise levels at higher frequencies. In this paper, the detailed design, complex fabrication processes, and thorough experimental validation are presented, demonstrating substantial performance enhancement potentials. A hybrid disk resonator with a single side-supporting anchor achieved an outstanding loaded Q-factor higher than 28,000 when operating under a capacitive drive and piezoelectric sense configuration. This is comparably higher than the measured Q-factor of 7600 for another disk resonator with two side-supporting anchors. The hybrid resonator exhibits a high Q-factor at its resonance frequency at 20 MHz, representing 2-fold improvement over the highest reported Q-factor for similar MEMS resonators in the literature. Also, the dual-transduction approach resulted in a more than 30 dB improvement in feedthrough suppression for devices with a 500 nm-thick ZnO layer, while hybrid resonators with a thicker piezoelectric layer of 1300 nm realized an even greater feedthrough suppression of more than 50 dB. The hybrid resonator integration strategy discussed offers an innovative solution for current and future advanced RF front-end applications, providing a versatile platform for future innovations in on-chip resonator technology. This work has the potential to lead to advancements in MEMS resonator technology, facilitating some significant improvements in multi-frequency and frequency agile RF applications through the original designs equipped with integrated capacitive and piezoelectric transduction mechanisms. The hybrid design also results in remarkable performance metrics, making it an ideal candidate for integrating next-generation wireless communication devices where size, cost, and energy efficiency are critical.

Selective Etch for Micromachining Process in Manufacturing Hybrid Microdevices composed of Ni-Mn-Ga and Silicon Layers

The goal of this study is to make selective etch possible for the next generation of MEMS(microelectromechanical systems) devices that are composed Ni-Mn-Ga and silicon layers. Due tothe large magnetic-field-induced strains of Ni-Mn-Ga, sensing and actuating components can be fab-ricated in the Ni-Mn-Ga layers. Other functional components can be manufactured in the silicon layer.Single crystalline Ni-Mn-Ga alloys that are grown by using the Bridgman vertical growth techniquehave so far obtained the largest magnetic field-induced strain (MFIS), a magnetic shape memory(MSM) effect. Similar to silicon wafers, Ni-Mn-Ga wafers are also sliced from crystal-oriented singlecrystalline ingots. To fabricate hybrid MEMS devices such as micromanipulators and robots, lab-on-chip containing micropump manifolds and valves, or vibration energy harvesters, the fabricationprocesses used for MEMS devices will be also used to fabricate components in the Ni-Mn-Ga layer ofthe hybrid MEMS devices. One of the most important processes for MEMS fabrication is the structur-ing of materials by chemical etching. The main goal of this study is to obtain evidence that the etchantetches silicon but not Ni-Mn-Ga and to identify an etchant that etches Ni-Mn-Ga but not silicon. Thepresent paper reports on a novel experiment in dissolving Ni-Mn-Ga alloys. An etchant compositionof 69% HNO3, 98% H2SO4, and CuSO4•5H2O is proposed for dissolving Ni-Mn-Ga alloys and thevariation in the dissolution rate by adjusting the concentrations of HNO3 and ultrapure water (UPW)is demonstrated. This etchant was demonstrated to etch Ni-Mn-Ga but not silicon. The HF+HNO3acidic solution commonly used for etching silicon does not dissolve Ni-Mn-Ga alloys.

Two-dimensional talc as a van der Waals material for solid lubrication at the nanoscale

Talc is a van der Waals and naturally abundant mineral with the chemical formula Mg3Si4O10(OH)2. Two-dimensional (2D) talc could be an alternative to hBN as van der Waals dielectric in 2D heterostructures. Furthermore, due to its good mechanical and frictional properties, 2D talc could be integrated into various hybrid microelectromechanical systems, or used as a functional filler in polymers. However, properties of talcas one of the main representatives of the phyllosilicate (sheet silicates) group are almost completely unexplored when ultrathin crystalline films and monolayers are considered. We investigate 2D talc flakes down to single layer thickness and reveal their efficiency for solid lubrication at the nanoscale. We demonstrate by atomic force microscopy based methods and contact angle measurements that several nanometer thick talc flakes have all properties necessary for efficient lubrication: a low adhesion, hydrophobic nature, and a low friction coefficient of 0.10 ± 0.02. Compared to the silicon-dioxide substrate, 2D talc flakes reduce friction by more than a factor of five, adhesion by around 20%, and energy dissipation by around 7%. Considering our findings, together with the natural abundance of talc, we put forward that 2D talc can be a cost-effective solid lubricant in micro- and nano-mechanical devices.

SPICE-Based Multiphysics Model to Analyze the Dynamics of Ferroelectric Negative-Capacitance–Electrostatic MEMS Hybrid Actuators

We propose a framework to model ferroelectric negative capacitance: electrostatic Micro Electro Mechanical Systems (MEMS) hybrid actuators and analyze their dynamic (step input) response. Using this framework, we report the first proposal for reduction in the dynamic pull-in and pull-out voltages of the hybrid actuators due to the negative capacitance of the ferroelectric. The proposed model also reveals the effect of ferroelectric thickness on the dynamic pull-in and pull-out voltages and the effect of ferroelectric damping on the energy dissipated during actuation. We infer from our analysis that the hybrid actuators are better than the standalone MEMS actuators in terms of operating voltage and energy dissipation. Further, we show that one can trade-off a small part of the reduction in actuation voltage to achieve identical pull-in times in the hybrid and standalone MEMS actuators, while still consuming substantially lower energy in the former as compared to the latter. The circuit compatibility of the proposed hybrid actuator model makes it suitable for analysis and evaluation of various heterogeneous systems consisting of hybrid MEMS actuators and other electronic devices.

Electromagnetic Vibrational Energy Harvester With Microfabricated Springs and Flexible Coils

In this article, an electromagnetic vibrational energy harvester (EVEH) device has been designed and fabricated based on the hybrid microelectromechanical system and flexible circuit technology. The designed EVEH is composed of a disc magnet suspended by four microfabricated silicon springs above a stack of high-density flexible planar coils. At a sinusoidal acceleration with a peak-to-peak amplitude of 1 g, an output peak-to-peak voltage of 208.3 mV, and an output power of 10.5 μW are measured at the resonant frequency of 143 Hz. At an elevated acceleration of 7 g, a maximum output peak-to-peak voltage of 333.1 mV is realized with an increased magnet-coil distance of 0.65 mm.

Highly piezoresistive hybrid MEMS sensors

A flexible organic piezoresistive micro-electro-mechanical system (MEMS) strain sensor with enhanced sensitivity is presented. The piezoresistive transducers consist in CNT/SU-8 nanocomposites. The electrical resistance changes versus strain of CNT/SU-8 piezoresistive materials have shown linear and non-linear regions at low and high strain levels, respectively. The measurements have been correlated with an existing analytical model showing good agreement. This work also highlights the role of the MEMS design in the enhancement of the final sensing performance of the devices. The gauge factor calculated from the change of resistance as a function of applied strain has been found to reach 200 for optimized sensor geometries, providing highly sensitive piezoresistive strain sensors for flexible electronic applications.

MEMS-based miniature near-infrared spectrometer for application in environmental and food monitoring

Abstract We present a hybrid MEMS (micro-electromechanical systems) based spectrometer of the size of a sugar cube, fabricated at the clean room facilities of Fraunhofer IPMS, Dresden. This SGS (scanning grating spectrometer) is designed for integrated spectroscopic applications in the field of food quality analysis and food processing technology. Using another, larger, MEMS-based scanning grating spectrometer, we perform a series of test measurements of the absorption of different types of oil. Thereby, we demonstrate the suitability of this larger MEMS-based SGS for food quality analysis and establish a set of reference measurements. The optical parameters of the sugar cube-sized SGS are then evaluated against the requirements established in the above reference measurements. The spectral resolution of this device is still not sufficient for application in the near infrared, owing to the inaccuracy of one particular production step. Once these changes are in place, we are confident to achieve resolutions below 20 nm. In conclusion, we propose the miniaturised SGS as a mobile spectrometer for in- situ analysis integrated with a data processing system.

Single-Device and On-Chip Feedthrough Cancellation for Hybrid MEMS Resonators

Microelectromechanical systems (MEMS) resonators typically exhibit large parasitic feedthrough where the input drive signal is directly coupled to the output ports, presenting a challenge to full electrical characterization of resonators where the output is heavily embedded in feedthrough. We here present an on-chip solution that significantly mitigates the undesirable effects of parasitic feedthrough but using only a single device. We have demonstrated its use in a symmetrical mode of vibration (the extensional mode of a square-plate MEMS resonator) to show its applicability to most generic resonator mode shapes. In our measurements, we show that the proposed method for feedthrough cancellation provides a 40-dB common-mode rejection compared to when no feedthrough cancellation is implemented. The necessary matching of drive circuit capacitances is achieved by properly sizing and placing a dummy pad in the vicinity of each drive pad. The studies reported herein demonstrate that the integrity of the output signal from a MEMS resonator is not only determined by device dimensions but also strongly influenced by the interaction between fringing fields radiating from electrodes in proximity. These results could open up a new avenue in the design of hybrid MEMS resonant devices where the issue of feedthrough can be both effectively and cheaply addressed.

Development of a Hybrid MEMS BLDC Micromotor

This paper addresses the design of a new hybrid microelectromechanical systems (MEMS) micromotor. It is a small three-phase axial flux brushless dc (BLDC) motor. The stator is developed following the almost-standard CMOS technology rules used for MEMS manufacturing, and the coils have two copper layers. The rotor is made of a ring permanent magnet assembled over the stator chip. The stator design has been performed using an analytical model also presented in this paper. The microfabrication of the first prototypes is presented, followed by their characterization. With an efficiency of about 42% for an input power of 310 nW, this MEMS micromotor has very good performance and demonstrates the potential of electromagnetic systems at this scale.

Vortex Anemometer Using MEMS Cantilever Sensor

This paper presents construction and performance of a novel hybrid microelectromechanical system (MEMS) vortex flowmeter. A miniature cantilever MEMS displacement sensor was used to detect frequency of vortices development. 3-mm-long silicon cantilever, protruding directly out of a trailing edge of a trapezoidal glass-epoxy composite bluff body was put into oscillatory motion by vortices shed alternately from side surfaces of the obstacle. Verified linear measurement range of the device extended from 5 to 22 m/s; however, it could be broadened in absence of external 50-Hz mains electrical interfering signal which required bandpass frequency-domain digital sensor signal processing. The MEMS vortex sensor proved its effectiveness in detection of semilaminar airflow velocity distribution in a 40-mm-diameter tubular pipe.

Passive Hybrid MEMS for High-Temperature Telemetric Measurements

A contactless sensor represents an attractive solution for high-temperature measurements in harsh environments, where the use of cables is not suitable, and where the temperature values are beyond those permitted by active electronic circuits. Temperature sensors have a wide variety of applications in automated processes for temperature control and regulation. This paper describes a passive sensing device suitable for high-temperature measurements consisting of a microfabricated temperature-sensitive variable capacitor and a planar inductor designed for high-temperature environments. Another readout inductor constitutes, together with the planar inductor, a telemetric system, which is a coupled transformer with the readout connected to the measurement electronics. The proposed passive hybrid microelectromechanical systems (MEMS) consists of an interdigitated capacitor bonded to the planar inductor. The hybrid sensor behaves as an LC resonant circuit in which the interdigitated capacitor represents the capacitance and the planar inductor is the inductance. The temperature induces a displacement of the conductive electrodes of the interdigitated capacitor toward the fixed electrodes realizing a temperature-sensitive variable capacitor. An equivalent circuit scheme of the variable capacitor and the planar inductor has been analyzed. Two telemetric measurement methods, relying on a frequency variation output, have been tested. The whole system has been tested in the laboratory, and several results are reported. Finally, the sensor prototype was fabricated and successfully characterized up to 330?C as a proof of concept of temperature sensing through passive wireless communication. The proposed telemetric temperature system can be a solution for efficiency monitoring and predictive maintenance for harsh and complex environments, thereby eliminating the need for physical contacts, active elements, or power supplies, which cannot withstand harsh environments.

A Hybrid MEMS–Fiber Optic Tunable Fabry–Perot Filter

This paper describes a bulk-micromachined electrostatically tunable Fabry-Perot interferometric filter. The device is a hybrid optical filter combining fiber optics and microelectromechanical systems (MEMS) technologies. The static mirror is a Bragg grating mirror built on the end face of an optical fiber that is integrated with a MEMS device, which includes the tunable gold-coated mirror. The MEMS device is fabricated in ¿100¿-oriented silicon wafers using modified and optimized batch MEMS processes. A two-stage approach was used to achieve high finesse (F) and broad tunability simultaneously. In the first stage, actuator issues and mirror structural defects were corrected for by optimizing the fabrication-process parameters. In this stage, near-theoretical performance has been achieved with a pure Si MEMS tunable etalon. In stage two, optical fibers with dielectric stack mirrors from Micron Optics, Inc. have been integrated with the MEMS devices to form tunable cavities. The device insertion loss was below 15 dB and was mostly attributed to absorption losses in the gold coating. We measured a pass bandwidth of around 0.54 nm and a tuning range of nearly 120 nm resulting in an F of over 220.

Large area, freestanding GaN nanocolumn membrane with bottom subwavelength nanostructure

We propose, fabricate and characterize the freestanding GaN nanocolumn membrane with bottom subwavelength nanostructures. The GaN nanocolumns are epitaxially grown on freestanding nanostructured silicon substrate that is achieved by a combination of self-assemble technique and silicon-on-insulator (SOI) technology. Optical reflection is greatly suppressed in the visible range due to the graded refractive index effect of subwavelength nanostructures. The freestanding GaN nanocolumn membrane is realized by removing silicon substrate from the backside, eliminating the silicon absorption of the emitted light and leading to a strong blue emission from the bottom side. The obtained structures also demonstrate the potential application for anti-reflective (AR) coating and GaN-Si hybrid microelectromechanical system (MEMS).

Adhesion Forces Controlled by Chemical Self-Assembly and pH: Application to Robotic Microhandling

Robotic microhandling is a promising way to assemble microcomponents in order to manufacture a new generation of hybrid microelectromechanical systems. However, at the scale of several micrometers, the adhesion phenomenon highly perturbs the micro-object release and positioning. This phenomenon is directly linked to both the object and the gripper surface chemical composition. We propose to control the adhesion by using a chemical self-assembled monolayer on both surfaces. Different types of chemical functionalization have been tested, and this paper focuses on the presentation of aminosilane-grafted 3-(ethoxydimethylsilyl)propylamine and (3-aminopropyl)triethoxysilane. We show that the liquid pH can be used to modify the adhesion and to switch from an attractive behavior to a repulsive behavior. The pH control can thus be used to increase the adhesion during handling and cancel the adhesion during release. Experiments have shown that the pH control is able to control the release of a micro-object. This paper shows the relevance of a new type of reliable submerged robotic microhandling principle, which is based on adjustment of the chemical properties of the liquid.

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.

MEMS Retro-Phase-Modulator for Free-Space Coherent Optical Communications

This paper describes an electrostatically actuated microelectromechanical systems (MEMS) device combined with small-scale retroreflective elements to produce a hybrid MEMS retro-phase-modulator suitable for use in a retroreflective free-space coherent optical communications system. In contrast to other MEMS retromodulators reported, which have concentrated on intensity modulation, the device reported in this paper produces an optical phase modulation. Two types of retroreflective elements, namely, a ball lens and an off-the-shelf retroreflective strip have been incorporated into the modulator. This paper reports a transmission system operating at higher bit rates than those that were previously published for similar schemes. Modulation has been achieved at 400 bits/s with a transmission cost of 80 pJ/bit

Optomechatronic Design of Microassembly Systems for Manufacturing Hybrid Microsystems

Microassembly systems are a class of representative optomechatronic systems that play a critical role in the fabrication, packaging, and interconnection of hybrid microsystems such as hybrid microelectromechanical systems. Optomechatronic integration is essential to the development of microassembly systems due to the basic importance of microscope optics to microassembly. In this paper, the role of microscope optics in microassembly systems is analyzed. The general architecture of microassembly systems is introduced. Unique properties of microscale optomechatronics that differ from macroscale optomechatronics are summarized. These fundamental differences motivate the definition and discussion of microoptomechatronics. Major methodology issues in optomechatronic design of microassembly systems are introduced using examples. A wavelet-based microscopic image segmentation technique is presented to demonstrate the strength of using the unique properties of microoptomechatronics in microscopic image information processing.

Advancement in low melting solder deposition by pulsed Magnetron Sputter-PVD process for microsystemtechnology

Micro-Electro Mechanical Systems (MEMS) are in general use today, either as product upgrading like airbag sensors or as independent microsystem like ink jet printer heads. The main application fields of microsystems are information technology, medicine, biochemistry, automotive industries and telecommunication. The components of these MEMS consist of various materials, which have to be joined. To join materials like ceramics, synthetic materials or metals to a hybrid MEMS established joining technologies have to be adjusted. For the assembling and mounting of temperature sensitive micro-components, a low temperature joining process, like the Transient Liquid Phase (TLP) bonding, is needed.The TLP-Bonding process combines the characteristics of liquid-phase joining (soldering and brazing) with diffusion bonding. The TLP solder system is a binary multilayer system of thin films. One film possesses a high (e.g. Cu, Au) and the other a low (e.g. Sn, In) melting point. During heating, the low melting component diffuses into the high melting component and forms an intermetallic phase, raising the remelting temperature of the system. The multilayer system was deposited by a pulsed Magnetron Sputter (MS)-PVD process.In former investigations, the TLP systems Cu–Sn and Cu–In showed high potential for joining operations in microsystems. The benefit of these systems is the combination of the low melting elements to the eutectic alloy SnIn. For this low melting alloy, the substrate temperature as well as the target temperature is of interest. The substrate temperatures were set and controlled by an additional cooling unit which was integrated into the sputtering facility. The target temperature is minimized by use of a pulsed power supply for deposition. The effects of different pulse rates and substrate temperatures to the microstructure and the soldering suitability of the TLP solder systems were investigated by scanning electron microscopy (SEM), nanoindentation and soldering tests.

Travel range extension of a MEMS electrostatic microactuator

Electrostatic comb microactuators have had a fundamental limitation in that the allowable travel range is limited to one-third of the total gap between comb fingers. Travel beyond this allowable range results in "pull-in" instability, independent of mechanical design parameters such as stiffness and mass. This brief focuses on the development of an active control system that stabilizes the actuator and allows travel almost over the entire available gap between comb fingers. The challenges to be addressed include the nonlinear dynamics of the actuator and system parameters that vary with each fabricated device. A nonlinear model inversion technique is used to address the nonlinear dynamics of the system. An adaptive controller is developed to provide improved position tracking in the presence of fabrication imperfections. The developed control system is then implemented on a special microelectromechanical systems (MEMS) electrostatic microactuator fabricated using deep reactive ion etching (DRIE) on silicon-on-insulator (SOI) wafers. The use of DRIE allows the fabrication of a high aspect ratio device that can produce large electrostatic forces with low actuation voltages. Experimental results presented in the brief show that the resulting system is capable of traveling 4.0 /spl mu/m over a 4.5 /spl mu/m full range without "pull in." Good tracking performance is obtained over a wide frequency band. Potential applications of the actuator are in the manipulation of subcellular structures within biological cells, microassembly of hybrid MEMS devices, and manipulation of large molecules such as DNA or proteins.

Solder deposition for transient liquid phase (TLP)-bonding by MSIP-PVD-process

In different technical areas micro electro mechanical systems (MEMS) are in use today. The components of these MEMS. consist of various materials, which are joined together. To join materials like ceramics, plastics or metals to a hybrid MEMS. a low temperature joining process, e.g. transient liquid phase (TLP) or an active soft soldering process can be performed. In this article, the TLP solder system is a binary multilayer system of thin films. One of the films had a high (Cu) and the other a low (In) melting point. The layer system was deposited with a magnetron sputter ion plating (MSIP)-PVD-process. In this article, the deposition of the low melting component indium with an active substrate cooling is presented. The substrate temperatures were set and controlled by an additional cooling unit, which was integrated into the sputtering facility. In the performed experiments a substrate temperature range from −40 °C to room temperature was investigated. The effects of these different substrate temperatures to the microstructure and the soldering suitability of the TLP solder systems were investigated by scanning electron microscopy (SEM), nanoindentation and soldering tests. In this article it was shown that Cu–In–TLP solder systems deposited with cooling periods showed an insufficient solder ability due to the Surface roughness. Solder systems deposited at low substrate temperatures set with a cooling unit showed a good solder ability. Also, the layer structure became amorphous, dense and homogenous.