Showing papers on "Anodic bonding published in 2021"

A Row-Column (RC) Addressed 2-D Capacitive Micromachined Ultrasonic Transducer (CMUT) Array on a Glass Substrate

Abstract: This article presents a row-column (RC) capacitive micromachined ultrasonic transducer (CMUT) array fabricated using anodic bonding on a borosilicate glass substrate. This is shown to reduce the bottom electrode-to-substrate capacitive coupling. This subsequently improves the relative response of the elements when top or bottom electrodes are used as the “signal” (active) electrode. This results in a more uniform performance for the two cases. Measured capacitance and resonant frequency, pulse-echo signal amplitude, and frequency response are presented to support this. Biasing configurations with varying ac and dc arrangements are applied and subsequently explored. Setting the net dc bias voltage across an off element to zero is found to be most effective to minimize spurious transmission. To achieve this, a custom switching circuit was designed and implemented. This circuit was also used to obtain orthogonal B-mode cross-sectional images of a rotationally asymmetric target.

Laser-assisted etching of borosilicate glass in potassium hydroxide

Abstract: We present a method for the selective etching of borosilicate glass (SCHOTT Borofloat 33), in which we modify the glass with an ultrashort pulse laser and subsequent wet chemical etching. The BF33 glass is often used in microtechnology to produce sensors, actors, and fluidic chips as it can be bonded to silicon wafers by anodic bonding. The glass is irradiated and modified by circular polarized laser light with a wavelength of 1030 nm. By etching the glass with potassium hydroxide, the modified material can be removed. In this study, the selectivity was analyzed dependent on the laser parameters pulse repetition rate, pulse duration, writing speeds, and pulse energy. A selectivity up to 540 could be observed in this study. Finally, the manufacturing capabilities for three-dimensional free form shapes in BF33 are demonstrated and compared with fused silica.

High-Consistency Optical Fiber Fabry-Perot Pressure Sensor Based on Silicon MEMS Technology for High Temperature Environment.

Abstract: This paper proposes a high-temperature optical fiber Fabry–Perot pressure sensor based on the micro-electro-mechanical system (MEMS). The sensing structure of the sensor is composed of Pyrex glass wafer and silicon wafer manufactured by mass micromachining through anodic bonding process. The separated sensing head and the gold-plated fiber are welded together by a carbon dioxide laser to form a fiber-optic Fabry–Perot high temperature pressure sensor, which uses a four-layer bonding technology to improve the sealing performance of the Fabry–Perot cavity. The test system of high temperature pressure sensor is set up, and the experimental data obtained are calculated and analyzed. The experimental results showed that the maximum linearity of the optical fiber pressure sensor was 1% in the temperature range of 20–400 °C. The pressure sensor exhibited a high linear sensitivity of about 1.38 nm/KPa at room temperature at a range of pressures from approximarely 0-to 1 MPa. The structure of the sensor is characterized by high consistency, which makes the structure more compact and the manufacturing process more controllable.

A Resonant Pressure Microsensor with a Wide Pressure Measurement Range.

Abstract: This paper presents a resonant pressure microsensor with a wide range of pressure measurements. The developed microsensor is mainly composed of a silicon-on-insulator (SOI) wafer to form pressure-sensing elements, and a silicon-on-glass (SOG) cap to form vacuum encapsulation. To realize a wide range of pressure measurements, silicon islands were deployed on the device layer of the SOI wafer to enhance equivalent stiffness and structural stability of the pressure-sensitive diaphragm. Moreover, a cylindrical vacuum cavity was deployed on the SOG cap with the purpose to decrease the stresses generated during the silicon-to-glass contact during pressure measurements. The fabrication processes mainly contained photolithography, deep reactive ion etching (DRIE), chemical mechanical planarization (CMP) and anodic bonding. According to the characterization experiments, the quality factors of the resonators were higher than 15,000 with pressure sensitivities of 0.51 Hz/kPa (resonator I), −1.75 Hz/kPa (resonator II) and temperature coefficients of frequency of 1.92 Hz/°C (resonator I), 1.98 Hz/°C (resonator II). Following temperature compensation, the fitting error of the microsensor was within the range of 0.006% FS and the measurement accuracy was as high as 0.017% FS in the pressure range of 200 ~ 7000 kPa and the temperature range of −40 °C to 80 °C.

The Design and Fabrication of the High Integrated Sensitive Electrodes by Adopting the Anodic Bonding Technology for the Electrochemical Seismic Sensors

Abstract: This paper developed a method to fabricate the MEMS based sensitive electrodes for the electrochemical seismic sensors with the anodic bonding technology. In comparison to previously reported counterparts, the proposed sensing electrodes adopted the three-layer bonding structure of silicon-glass-silicon applied as the substitute of multilayer manual assembly structure, which have the advantages of simplified assembly processes of sensing unit and high consistency as the no requirement of manual alignment. The results shown that the cross-correlation coefficient between two proposed devices was quantified as 0.9998 with the sensitivity of 5956 V/(m/s) @1Hz, it is able to achieve both high sensitivity and high integration.

The MEMS-Based Electrochemical Seismic Sensor With Integrated Sensitive Electrodes by Adopting Anodic Bonding Technology

Abstract: Seismic sensors are the key sensitive components in geophysical exploration, and the new-type electrochemical seismic sensors have gradually aroused researchers’ interest for their superior performance in low-frequency domain and large working inclination. In this paper, a method was developed to fabricate the MEMS (micro-electro-mechanical systems) based integrated electrodes for the electrochemical seismic sensors. The proposed integrated electrodes which employed three-layer anodic bonding structure of silicon-glass-silicon served as the substitutes for multilayer manual assembly structures. Compared to previous counterparts, this integrated structure has the advantages of simplified assembly processes of sensitive unit and high consistency as the no requirement of manual alignment. The results shown that the cross-correlation coefficient between two proposed devices was quantified as 0.998 with the sensitivity of 5956 V/(m/s) @1Hz. This electrode is so far the sensitive structure which realize both high sensitivity and high integration in the electrochemical seismic sensors.

Temperature Compensated Wide-Range Micro Pressure Sensor with Polyimide Anticorrosive Coating for Harsh Environment Applications

Abstract: In this work, a MEMS piezoresistive micro pressure sensor (1.5 × 1.5 × 0.82 mm) is designed and fabricated with SOI-based micromachining technology and assembled using anodic bonding technology. In order to optimize the linearity and sensitivity over a wide effective pressure range (0–5 MPa) and temperature range (25–125 °C), the diaphragm thickness and the insulation of piezoresistors are precisely controlled by an optimized micromachining process. The consistency of the four piezoresistors is greatly improved by optimizing the structure of the ohmic contact pads. Furthermore, the probability of piezoresistive breakdown during anodic bonding is greatly reduced by conducting the top and bottom silicon of the SOI. At room temperature, the pressure sensor with 40 µm diaphragm demonstrates reliable linearity (0.48% F.S.) and sensitivity (33.04 mV/MPa) over a wide pressure range of 0–5.0 MPa. In addition, a polyimide protection layer is fabricated on the top surface of the sensor to prevent it from corrosion by a moist marine environment. To overcome the linearity drift due to temperature variation in practice, a digital temperature compensation system is developed for the pressure sensor, which shows a maximum error of 0.43% F.S. in a temperature range of 25–125 °C.

Fabrication and characterisation of a silicon-borosilicate glass microfluidic device for synchrotron-based hard X-ray spectroscopy studies

Abstract: Some of the most fundamental chemical building blocks of life on Earth are the metal elements. X-ray absorption spectroscopy (XAS) is an element-specific technique that can analyse the local atomic and electronic structure of, for example, the active sites in catalysts and energy materials and allow the metal sites in biological samples to be identified and understood. A microfluidic device capable of withstanding the intense hard X-ray beams of a 4th generation synchrotron and harsh chemical sample conditions is presented in this work. The device is evaluated at the K-edges of iron and bromine and the L3-edge of lead, in both transmission and fluorescence mode detection and in a wide range of sample concentrations, as low as 0.001 M. The device is fabricated in silicon and glass with plasma etched microchannels defined in the silicon wafer before anodic bonding of the glass wafer into a complete device. The device is supported with a well-designed printed chip holder that made the microfluidic device portable and easy to handle. The chip holder plays a pivotal role in mounting the delicate microfluidic device on the beamline stage. Testing validated that the device was sufficiently robust to contain and flow through harsh acids and toxic samples. There was also no significant radiation damage to the device observed, despite focusing with intense X-ray beams for multiple hours. The quality of X-ray spectra collected is comparable to that from standard methods; hence we present a robust microfluidic device to analyse liquid samples using synchrotron XAS.

Short-Pulse Laser-Assisted Fabrication of a Si-SiO2 Microcooling Device.

Abstract: Thermal management is one of the main challenges in the most demanding detector technologies and for the future of microelectronics. Microfluidic cooling has been proposed as a fully integrated solution to the heat dissipation problem in modern high-power microelectronics. Traditional manufacturing of silicon-based microfluidic devices involves advanced, mask-based lithography techniques for surface patterning. The limited availability of such facilities prevents widespread development and use. We demonstrate the relevance of maskless laser writing to advantageously replace lithographic steps and provide a more prototype-friendly process flow. We use a 20 W infrared laser with a pulse duration of 50 ps to engrave and drill a 525 μm-thick silicon wafer. Anodic bonding to a SiO2 wafer is used to encapsulate the patterned surface. Mechanically clamped inlet/outlet connectors complete the fully operational microcooling device. The functionality of the device has been validated by thermofluidic measurements. Our approach constitutes a modular microfabrication solution that should facilitate prototyping studies of new concepts for co-designed electronics and microfluidics.

Low-Temperature Anodic Bonding for Wafer-Level Al–Al Interconnection in MEMS Grating Gyroscope

Abstract: In this article, low-temperature anode bonding technology is used to realize wafer-level Al–Al interconnection in MEMS grating gyroscope. The gyroscope structure was fabricated on silicon by micromachining process. Both Al wiring and Al grating were fabricated by magnetron sputtering. Before bonding, the bonded wafers were treated through Ar plasma. The wafer-level bonding was then performed at 330 °C for 15 min under 0.21 MPa with a dc voltage of 1000 V. Acoustic and interfacial tests showed a defect-free Al–Al interconnection. The average bonding strength was as high as 33.94 MPa and the measured resistance was approximate to the theoretical value. The bonded structure was also undamaged under 1500-g acceleration shock. It is concluded that the low-temperature anode bonding for wafer-level Al–Al interconnection will further promote the development of MEMS grating gyroscope.

A Miniature Ionization Vacuum Sensor With a SiOₓ-Based Tunneling Electron Source

Abstract: A miniature ionization vacuum sensor (IVS) based on an on-chip SiOx-based tunneling electron source is reported. The vacuum sensor fabricated by microfabrication technologies exhibits a compact multilayered structure with overall dimensions of $13\times 9\times2.7$ mm3, where the electron source chip, Si layer of the electron collector, Si layer of the ion collector, and glass spacers between them are stacked together by an anodic bonding method. Electron impact ionization occurs in a semiclosed cavity through the electron and ion collector layers and glass spacers. Because of the compact structure, low working voltage of SiOx-based tunneling electron sources, and stable electron emission of the electron sources in a poor vacuum, a wide linear detection range from $1.3\times 10^{-2}$ to 133 Pa and a sensitivity of $8.3\times 10^{-4}$ Pa−1 have been demonstrated for the devices. These advantages, including miniature size, a detection range up to the rough vacuum regime, and the capability of batch fabrication with microfabrication technologies, make our IVSs promising in vacuum measurements.

Design of Pre-Charged CMUTs with a Metal Floating Gate

Abstract: Capacitive micromachined ultrasonic transducers (CMUTs) require a DC bias voltage for efficient operation. Precharged CMUTs can eliminate the requirement of DC bias voltage, thus ease the design of frontend circuitry for transmit/receive operation. We used a metal floating gate structure to trap charges instead of an oxide-nitride interface or a silicon floating island. Because the potential barrier height for metal-oxide interface is much higher than oxide-nitride and oxide-silicon barrier heights, it is possible to retain trapped charge without leakage. Also we do not expect any charge leakage on the metal-nitride side because of the vacuum gap. We used an anodic bonding based process and formed the floating metal under the silicon plate where the metal is sandwiched between silicon dioxide and silicon nitride layers. Initial results show that the proposed structure can store electrical charges to allow operation without a DC bias. The CMUTs fabricated using the described approach will be primarily used as an ultrasound-powered implantable biomedical device.

Focused ion beam milling based formation of nanochannels in silicon-glass microfluidic chips for the study of ion transport

Abstract: Nowadays nanofluidic devices have a great potential in biosensing and DNA sequencing applications. This work is aimed at development of the technique for fabrication of arrays of nanochannels in silicon-glass chips by focused ion beam milling. The use of lithography with charged particles (electrons and ions) paves the way for the fabrication of micro- and nanochannels and pores as well as functional nanostructures of a more complex shape in nanofluidic devices. In this study, a technique for fabrication of microfluidic chips with a system of nanochannels connecting two independent volumes (2 half cells) was developed. It was shown experimentally that the focused ion beam etching time has an influence on both the width of the created nanochannels and their depth. We suggested using anodic bonding of a silicon wafer with the net of micro- and nanochannels with a glass plate for encapsulation of such devices that provide their long lifetime of microfluidic devices. To determine the functionality of the produced devices we studied the ionic conductivity of the produced nanochannels experimentally and using a theoretical approach. Analyzing the results, we determined the effective diameter of the nanochannels and the surface charge density inside the channel which were 20 nm and 1.5 mC/m $${}^2$$ , respectively. The proposed technique allows to create ensembles of channels with a predefined width and depth. Such systems can find wide application in studies of the transport phenomena of both ions and various molecules in nanofluidic devices.

Triboelectric nanogenerator-based anodic bonding of silicon to glass with an intermediate aluminum layer

Abstract: The application of anodic bonding with metal or alloy films as the intermediate layer in micro electromechanical systems (MEMS) is becoming more widespread. Simultaneously, the realization of lower bonding voltage and current is an urgent problem to be solved in anodic bonding, cause large voltages and currents can cause damage and failure to tiny devices of MEMS. Sputtering aluminum as an intermediate layer, well-bonded silicon to glass wafers can be obtained with lower bonding current by applying triboelectric nanogenerator (TENG) instead of traditional direct-current (DC) power supply for the first time. Meanwhile, the tensile strength of the bonded wafers with an intermediate aluminum layer is up to 20 MPa, which is comparable with the DC driven bonded strength and is also 50 % higher than that without the aluminum layer. The TENG-based anodic bonding of silicon to glass with an aluminum layer has good bonding quality, which exhibits potential usefulness for application in MEMS packing.

Ultra-low temperature anodic bonding of silicon and glass based on nano-gap dielectric barrier discharge

Abstract: The article improves the process of dielectric barrier discharge (DBD) activated anode bonding. The treated surface was characterized by the hydrophilic surface test. The results showed that the hydrophilic angle was significantly reduced under nano-gap conditions and the optimal discharge voltage was 2 kV Then, the anodic bonding and dielectric barrier discharge activated bonding were performed in comparison experiments, and the bonding strength was characterized by tensile failure test. The results showed that the bonding strength was higher under the nano-gap dielectric barrier discharge. This process completed 110 °C ultra-low temperature anodic bonding and the bonding strength reached 2 MPa. Finally, the mechanism of promoting bonding after activation is also discussed.

Measurement of DC and AC electric fields inside an atomic vapor cell with wall-integrated electrodes

Abstract: We present and characterize an atomic vapor cell with silicon ring electrodes directly embedded between borosilicate glass tubes. The cell is assembled with an anodic bonding method and is filled with Rb vapor. The ring electrodes can be externally connectorized for application of electric fields to the inside of the cell. An atom-based, all-optical, laser-spectroscopic field sensing method is employed to measure electric fields in the cell. Here, the Stark effect of electric-field-sensitive rubidium Rydberg atoms is exploited to measure DC electric fields in the cell of $\sim$5 V/cm, with a relative uncertainty of 10%. Measurement results are compared with DC field calculations, allowing us to quantify electric-field attenuation due to free surface charges inside the cell. We further measure the propagation of microwave fields into the cell, using Autler-Townes splitting of Rydberg levels as a field probe. Results are obtained for a range of microwave powers and polarization angles relative to the cell's ring electrodes. We compare the results with microwave-field calculations. Applications are discussed.

Physicochemical Processes in Alkaline Glass with Anodic Bonding of Glass and Silicon

Abstract: The physicochemical processes occurring in the structure of alkaline glass and at a silicon – glass interface with anodic bonding of the glass and silicon wafers were studied. The bonding of these materials is now widely used in industry in the development of sensitive elements of micromechanical sensors, such as pressure, acceleration, and other sensors. It is shown that in order to obtain a high-quality bond both the parameters of the technological process (for example, the applied voltage) and the structural features of the bonded parts (for example, the thickness of the glass wafers) can be varied.

Effect of rare earth oxide CeO2 on the anodic bonding performance of PEG-based MEMS encapsulation materials:

Abstract: Herein, we synthesized a new polyethylene glycol (PEG)-based solid polymer electrolyte containing a rare earth oxide, CeO2, using mechanical metallurgy to prepare an encapsulation bonding material ...

Self-encapsulated DC MEMS switch using recessed cantilever beam and anodic bonding between silicon and glass

Abstract: In the present work, we report design, fabrication and testing of a novel DC MEMS switch incorporating a self-encapsulated and recessed micro-cantilever beam. Wafer level anodic bonding with press-on contacts between silicon and glass is used innovatively to secure the recessed cantilever beam from one side. The cantilever is made of single crystal silicon in a recessed cavity whereas actuating electrode and signal lines are formed on corning glass. Anodic bonding provides “press on contacts” between silicon and glass plate and also secures the cantilever beam in the recessed cavity in silicon. The signal lines and pull-in electrode are formed on the glass plate using aluminium metallization while the cantilever has a gold pad at its tip. The anodic bonding provides three major advantages (i) it encapsulates the fragile beam and thus protects it from damage during dicing and packaging process (ii) it provides press-on contact between signal lines on glass plate and bonding pads on silicon (iii) it makes the beam optically visible. The devices were simulated using COMSOL multiphysics software and the results were compared with experimentally measured values. The cantilever based switch operates at low actuation voltage (average ~ 12 V) indicating that it can be used for power electronic circuits and various other applications.

Development and post-dicing wet release of MEMS magnetometer: an approach

Abstract: Si-based micro electro mechanical systems (MEMS) magnetometer does not require specialized magnetic materials avoiding magnetic hysteresis, ease in fabrication and low power consumption. It can be fabricated using the same processes used for gyroscope and accelerometer fabrication. The paper reports the dicing mechanism for the released MEMS xylophone magnetic sensor fabricated using wafer bonding technology and its characterization in ambient pressure and under vacuum conditions. The purpose of this paper is to dice the wafer bonded Si-magnetometer in a cost-effective way without the use of laser dicing and test it for Lorentz force transduction.,A xylophone bar MEMS magnetometer using Lorentz force transduction is developed. The fabricated MEMS-based xylophone bars in literature are approximately 500 µm. The present work shows the released structure (L = 592 µm) fabricated by anodic bonding technique using conducting Si as the structural layer and tested for Lorentz force transduction. The microstructures fabricated at the wafer level are released. Dicing these released structures using conventional diamond blade dicing may damage the structures and reduce the yield. To avoid the problem, positive photoresist S1813 was filled before dicing. The dicing of the wafer, filled with photoresist and later removal of photoresist post dicing, is proposed.,The devices realized are stiction free and straight. The dynamic measurements are done using laser Doppler vibrometer to verify the released structure and test its functionality for Lorentz force transduction. The magnetic field is applied using a permanent magnet and Helmholtz coil. Two sensors with quality factors 70 and 238 are tested with resonant frequency 112.38 kHz and 114.38 kHz, respectively. The sensor D2, with Q as 238, shows a mechanical sensitivity of 500 pm/Gauss and theoretical Brownian noise-limited resolution of 53 nT/vHz.,The methodology and the study will help develop Lorentz force–based MEMS magnetometers such that stiction-free structures are released using wet etch after the mechanical dicing.

Construction of a spherically bent crystal analyzer through anodic bonding for a non-resonant inelastic X-ray scattering spectrometer

Abstract: The anodic bonding method was used to construct spherically bent crystal analyzers for a synchrotron radiation based non-resonant inelastic X-ray scattering spectrometer to probe the local electron...

A Resonant Differential Pressure Microsensor With a Stress Isolation Layer

Abstract: This article presents a resonant differential pressure microsensor with a stress isolation layer, which is mainly composed of three parts, an SOI wafer, including a handle layer, an oxide layer and a device layer, a GOS wafer, including a glass layer and a silicon layer and a stress isolation structure, including a two-layer glass. The SOI device layer including the central beam in the central area and the side beam in the side area is bonded to GOS glass wafer for vacuum packaging of the beams. The diaphragm including SOI device layer and the GOS wafer is coupled to the two beams through anchors. In order to realize stress isolation, the glass base is designed as a convex structure, which is bonded to sensor chip by anodic bonding technology and fixed to Kovar pedestal by epoxy glue, respectively. Experimental characterizations were carried out, indicating differential pressure sensitivity of - 144.85 Hz/kPa (∼2079 ppm/kPa) and static pressure sensitivity of −0.98 Hz/kPa (∼14 ppm/kPa) and temperature sensitivity of −2.19 Hz/°C (∼31 ppm/°C). Compared with existing research, the low temperature sensitivity was realized, improving the temperature long-term stability of the sensor.