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Micromachines
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Design, Fabrication, Testing of MEMS/NEMS
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Design, Fabrication, Testing of MEMS/NEMS

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "A：Physics".

Deadline for manuscript submissions: closed (30 December 2022) | Viewed by 33329

Special Issue Editors

Dr. Nan Wang

E-Mail Website
Guest Editor
Institute of Microelectronics, A*STAR, Singapore 138632, Singapore
Interests: MEMS; RF-MEMS; piezoelectric; resonator; acoustic filters; MEMS sensors; micro-fabrication process
Special Issues, Collections and Topics in MDPI journals
Dr. Tao Wu

E-Mail Website
Guest Editor
Microsystem and Non-Linear transducers Laboratory, ShanghaiTech University, Shanghai 201210, China
Interests: piezoelectric MEMS resonators; multiferroic transducers; MEMS sensors and microsystems
Special Issues, Collections and Topics in MDPI journals
Dr. Jicong Zhao

E-Mail Website
Guest Editor
School of Information Science and Technology, Nantong University, Nantong 226019, China
Interests: MEMS resonators; MEMS infrared detectors; micro-fabrication process; MEMS packaging
Special Issues, Collections and Topics in MDPI journals
Dr. Chen Liu

E-Mail Website
Guest Editor
Institute of Microelectronics, A*STAR, Singapore 138632, Singapore
Interests: RF-MEMS resonators; filters; phase shifters

Special Issue Information

Dear Colleagues,

Nowadays, micro-electromechanical systems (MEMS) technology has witnessed rapid development and innovative progress, which cover a full spectrum of applications from IoT (Internet of Things) to wearable systems. Remarkable advances are contributed in MEMS devices including physical sensors, chemical sensors, biosensors, optical sensors, RF MEMS and self-power devices, etc., which have great potential to reshape an intelligent future world.

Here, this Special Issue aims to highlight recent novel progresses in cutting-edge MEMS device technologies, including original research articles and topical reviews in the scope of materials, design and fabrication technologies, characterization methods, packaging and microsystem integration solutions. We would like to encourage our colleagues to contribute their excellent work to this Special Issue.

The topics of this Special Issue include, but are not limited to:

  1. Novel functional MEMS materials;
  2. Innovative MEMS mechanical and chemical sensors;
  3. Biological devices for wearable healthcare systems;
  4. Optical and quantum MEMS devices and systems;
  5. RF MEMS for telecommunication systems;
  6. MEMS devices for self-powered systems;
  7. Micro/nano fabrication process and integration;
  8. MEMS packaging and reliability issues.

Dr. Nan Wang
Dr. Tao Wu
Dr. Jicong Zhao
Dr. Chen Liu
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • functional MEMS materials
  • MEMS sensors
  • MEMS Optical and quantum MEMS devices
  • RF MEMS devices
  • energy harvesting devices
  • MEMS fabrication and integration
  • MEMS packaging and testing

Related Special Issue

Published Papers (17 papers)

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Research

14 pages, 6500 KiB  
Article
Visible Pulsed Laser-Assisted Selective Killing of Cancer Cells with PVP-Capped Plasmonic Gold Nanostars
by Aniket Mishra, Rafia Inaam, Shunya Okamoto, Takayuki Shibata, Tuhin Subhra Santra and Moeto Nagai
Micromachines 2023, 14(6), 1173; https://doi.org/10.3390/mi14061173 - 31 May 2023
Cited by 1 | Viewed by 1393
Abstract
A new generation of nanoscale photosensitizer agents has improved photothermal capabilities, which has increased the impact of photothermal treatments (PTTs) in cancer therapy. Gold nanostars (GNS) are promising for more efficient and less invasive PTTs than gold nanoparticles. However, the combination of GNS [...] Read more.
A new generation of nanoscale photosensitizer agents has improved photothermal capabilities, which has increased the impact of photothermal treatments (PTTs) in cancer therapy. Gold nanostars (GNS) are promising for more efficient and less invasive PTTs than gold nanoparticles. However, the combination of GNS and visible pulsed lasers remains unexplored. This article reports the use of a 532 nm nanosecond pulse laser and polyvinylpyrrolidone (PVP)-capped GNS to kill cancer cells with location-specific exposure. Biocompatible GNS were synthesized via a simple method and were characterized under FESEM, UV–visible spectroscopy, XRD analysis, and particle size analysis. GNS were incubated over a layer of cancer cells that were grown in a glass Petri dish. A nanosecond pulsed laser was irradiated on the cell layer, and cell death was verified via propidium iodide (PI) staining. We assessed the effectiveness of single-pulse spot irradiation and multiple-pulse laser scanning irradiation in inducing cell death. Since the site of cell killing can be accurately chosen with a nanosecond pulse laser, this technique will help minimize damage to the cells around the target cells. Full article
(This article belongs to the Special Issue Design, Fabrication, Testing of MEMS/NEMS)
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42 pages, 8323 KiB  
Article
Investigation and Research of High-Performance RF MEMS Switches for Use in the 5G RF Front-End Modules
by Alexey Tkachenko, Igor Lysenko and Andrey Kovalev
Micromachines 2023, 14(2), 477; https://doi.org/10.3390/mi14020477 - 18 Feb 2023
Cited by 6 | Viewed by 1838
Abstract
In this article, based on the developed methodology, the stages of designing two designs of high-performance radio-frequency single-pole single-throw microelectromechanical switches are investigated. These radio-frequency microelectromechanical switches are designed to operate at a central resonant frequency of 3.6 GHz and 3.4 GHz, respectively, [...] Read more.
In this article, based on the developed methodology, the stages of designing two designs of high-performance radio-frequency single-pole single-throw microelectromechanical switches are investigated. These radio-frequency microelectromechanical switches are designed to operate at a central resonant frequency of 3.6 GHz and 3.4 GHz, respectively, as well as to work both in mobile communication devices and in the design of the architecture of 5G mobile networks, in particular in arrays of integrated antennas and radio-frequency interface modules. The manufacture and study of two designed structures are researched. For the first manufactured experimental sample in the open state the insertion loss is no more than −0.69 dB and the reflection loss is −28.35 dB, and in the closed state the isolation value is at least −54.77 dB at a central resonant frequency of 3.6 GHz. For the second in the open state the value of the insertion loss is no more than −0.67 dB and the reflection loss is −20.7 dB, and in the closed state the isolation value is not less than −52.13 dB at the central resonant frequency of 3.4 GHz. Both manufactured experimental samples are characterized by high linearity, as well as a small value of contact resistance in the closed state. Full article
(This article belongs to the Special Issue Design, Fabrication, Testing of MEMS/NEMS)
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15 pages, 8209 KiB  
Article
A Phase Canceling Technique to Improve SAW Duplexer Isolation
by Jianbin Tao, Zhengjie Tang, Yali Zou, Bin Wang, Jiawei Li, Yuhao Liu and Tao Wu
Micromachines 2023, 14(2), 239; https://doi.org/10.3390/mi14020239 - 17 Jan 2023
Cited by 2 | Viewed by 1373
Abstract
Spectrum resources are becoming increasingly crowded, and the isolation interval between different systems is getting smaller and smaller. This puts forward higher requirements for the duplexer. The duplexer is an important part of the radio frequency front end, and the isolation requirement is [...] Read more.
Spectrum resources are becoming increasingly crowded, and the isolation interval between different systems is getting smaller and smaller. This puts forward higher requirements for the duplexer. The duplexer is an important part of the radio frequency front end, and the isolation requirement is becoming higher. This paper presents a phase canceling circuit to improve the performance of the duplexer to meet the requirement of the communication system for isolation. A phase canceling circuit is an effective method to enhance the isolation through use of a surface acoustic wave (SAW) on-chip circuit. It contains a duplexer and a branch. The branch is designed for diminishing the leakage signal of the duplexer. Compared with the leakage signal, the branch consists of two attenuators and a phase shifter to generate a signal which has equal extent and reverse phase. As a result, this method is capable of increasing the isolation of band 5 by 12 dB in the downlink frequency. Meanwhile, it neither affects other factors, such as insertion loss or return loss, nor increases the size of the chip. The phase canceling circuit is expected to promote the quality of duplexer to satisfy the strict requirements in 4G and 5G systems. Full article
(This article belongs to the Special Issue Design, Fabrication, Testing of MEMS/NEMS)
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14 pages, 4189 KiB  
Article
Improvement of YX42° Cut LiTaO3 SAW Filters with Optical Proximity Effect Correction Method
by Ping Luo, Yali Zou, Xinyu Yang, Juntao Li, Xuan Huang, Jian Zhou, Xing Han, Yushuai Liu, Yuhao Liu and Tao Wu
Micromachines 2023, 14(1), 205; https://doi.org/10.3390/mi14010205 - 13 Jan 2023
Cited by 1 | Viewed by 1865
Abstract
Due to the influence of the optical proximity effect (OPE), it is easy for a pattern of photoresistance to be inconsistent with a design pattern, thus damaging the performance of a SAW resonator. To solve this problem, this paper proposes an optimization method [...] Read more.
Due to the influence of the optical proximity effect (OPE), it is easy for a pattern of photoresistance to be inconsistent with a design pattern, thus damaging the performance of a SAW resonator. To solve this problem, this paper proposes an optimization method for SAW filters based on optical proximity correction (OPC). This method can avoid the tip discharge problem of SAW filters by suppressing the problem of rounding and shrinking of dummy electrode and electrode tail caused by OPE. This method increases the quality factor (Q) of the SAW resonator and thus decreases the insertion loss of the SAW filter. The filter increases the bandwidth by 1.8 MHz at −1.5 dB after applying the OPC method. Additionally, it improves the stability of the filter under high power conditions. Full article
(This article belongs to the Special Issue Design, Fabrication, Testing of MEMS/NEMS)
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13 pages, 5010 KiB  
Article
Process Optimization and Performance Evaluation of TSV Arrays for High Voltage Application
by Liuhaodong Feng, Shuwen Zeng, Yongquan Su, Lihao Wang, Yang Xu, Song Guo, Shuo Chen, Yucheng Ji, Xinlin Peng, Zhenyu Wu and Shinan Wang
Micromachines 2023, 14(1), 102; https://doi.org/10.3390/mi14010102 - 30 Dec 2022
Cited by 2 | Viewed by 1983
Abstract
In order to obtain high-quality through-silicon via (TSV) arrays for high voltage applications, we optimized the fabrication processes of the Si holes, evaluated the dielectric layers, carried out hole filling by Cu plating, and detected the final structure and electric properties of the [...] Read more.
In order to obtain high-quality through-silicon via (TSV) arrays for high voltage applications, we optimized the fabrication processes of the Si holes, evaluated the dielectric layers, carried out hole filling by Cu plating, and detected the final structure and electric properties of the TSVs. The Si through-hole array was fabricated in an 8-inch Si substrate as follows: First, a blind Si hole array was formed by the Si deep reactive etching (DRIE) technique using the Bosch process, but with the largest width of the top scallops reduced to 540 nm and the largest notch elimidiameternated by backside grinding, which also opens the bottom ends of the Si blind holes and forms 500-μm-deep Si through holes. Then, the sidewalls of the Si holes were further smoothed by a combination of thermal oxidation and wet etching of the thermal oxide. The insulating capability of the dielectric layers was evaluated prior to metal filling by using a test kit. The metal filling of the through holes was carried out by bottom-up Cu electroplating and followed by annealing at 300 °C for 1 h to release the electroplating stress and to prevent possible large metal thermal expansion in subsequent high-temperature processes. The TSV arrays with different hole diameters and spacing were detected: no visible defects or structure peeling was found by scanning electron microscopy (SEM) observations, and no detectable interdiffusion between Cu and the dielectric layers was detected by energy dispersive X-ray (EDX) analyses. Electric tests indicated that the leakage currents between two adjacent TSVs were as low as 6.80 × 10−10 A when a DC voltage was ramped up from 0 to 350 V, and 2.86 × 10−9 A after a DC voltage was kept at 100 V for 200 s. Full article
(This article belongs to the Special Issue Design, Fabrication, Testing of MEMS/NEMS)
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13 pages, 14364 KiB  
Article
Bimorph Dual-Electrode ScAlN PMUT with Two Terminal Connections
by Meilin Ji, Haolin Yang, Yongxin Zhou, Xueying Xiu, Haochen Lv and Songsong Zhang
Micromachines 2022, 13(12), 2260; https://doi.org/10.3390/mi13122260 - 19 Dec 2022
Cited by 6 | Viewed by 2602
Abstract
This paper presents a novel bimorph Piezoelectric Micromachined Ultrasonic Transducer (PMUT) fabricated with 8-inch standard CMOS-compatible processes. The bimorph structure consists of two layers of 20% scandium-doped aluminum nitride (Sc0.2Al0.8N) thin films, which are sandwiched among three molybdenum (Mo) [...] Read more.
This paper presents a novel bimorph Piezoelectric Micromachined Ultrasonic Transducer (PMUT) fabricated with 8-inch standard CMOS-compatible processes. The bimorph structure consists of two layers of 20% scandium-doped aluminum nitride (Sc0.2Al0.8N) thin films, which are sandwiched among three molybdenum (Mo) layers. All three Mo layers are segmented to form the outer ring and inner plate electrodes. Both top and bottom electrodes on the outer ring are electrically linked to the center inner plate electrodes. Likewise, the top and bottom center plate electrodes are electrically connected to the outer ring in the same fashion. This electrical configuration maximizes the effective area of the given PMUT design and improves efficiency during the electromechanical coupling process. In addition, the proposed bimorph structure further simplifies the device’s electrical layout with only two-terminal connections as reported in many conventional unimorph PMUTs. The mechanical and acoustic measurements are conducted to verify the device’s performance improvement. The dynamic mechanical displacement and acoustic output under a low driving voltage (1 Vpp) are more than twice that reported from conventional unimorph devices with a similar resonant frequency. Moreover, the pulse-echo experiments indicate an improved receiving voltage of 10 mV in comparison with the unimorph counterpart (4.8 mV). The validation of device advancement in the electromechanical coupling effect by using highly doped ScAlN thin film, the realization of the proposed bimorph PMUT on an 8-inch wafer paves the path to production of next generation, high-performance piezoelectric MEMS. Full article
(This article belongs to the Special Issue Design, Fabrication, Testing of MEMS/NEMS)
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12 pages, 4074 KiB  
Article
Structural Optimization and Mechanical Simulation of MEMS Thin-Film Getter–Heater Unit
by Xinlin Peng, Yucheng Ji, Shuo Chen, Song Guo, Liuhaodong Feng, Yang Xu and Shinan Wang
Micromachines 2022, 13(12), 2252; https://doi.org/10.3390/mi13122252 - 18 Dec 2022
Cited by 1 | Viewed by 1484
Abstract
A MEMS thin-film getter–heater unit has been previously proposed for the vacuum packaging of a Micro-Electro-Mechanical System (MEMS) device, where the floating structure (FS) design is found to be obviously more power-efficient than the solid structure (SS) one by heat transfer capacity simulation. [...] Read more.
A MEMS thin-film getter–heater unit has been previously proposed for the vacuum packaging of a Micro-Electro-Mechanical System (MEMS) device, where the floating structure (FS) design is found to be obviously more power-efficient than the solid structure (SS) one by heat transfer capacity simulation. However, the mechanical strength of the FS is weaker than the SS by nature. For high temperature usage, the unit structure must be optimized in order to avoid fracture of the cantilever beam or film delamination due to strong excessive stress caused by heating. In this paper, COMSOL is used to simulate the stress and deformation of the MEMS thin-film getter–heater unit with the cantilever structure. By comparing various cantilever structures, it is found that a model with a symmetrically-shaped heater and edge–center-located cantilever model (II-ECLC model) is the most suitable. In this model, even when the structure is heated to about 600 °C, the maximum stress of the cantilever beam is only 455 MPa, much lower than the tensile strength of silicon nitride (Si3N4, 12 GPa), and the maximum deformation displacement is about 200 μm. Meanwhile, the interfacial stress between the getter and the insulating layer is 44 MPa, sufficiently lower than the adhesion strength between silicon nitride film and titanium film (400–1850 MPa). It is further found that both the stress of the cantilever structure and the interfacial stress between the getter and the insulating layer beneath increase linearly with temperature; and the deformation of the cantilever structure is proportional to its stress. This work gives guidance on the design of MEMS devices with cantilever structures and works in high temperature situations. Full article
(This article belongs to the Special Issue Design, Fabrication, Testing of MEMS/NEMS)
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14 pages, 3875 KiB  
Article
An SOI-Structured Piezoresistive Differential Pressure Sensor with High Performance
by Zebin Xu, Jiahui Yan, Meilin Ji, Yongxin Zhou, Dandan Wang, Yuanzhi Wang, Zhihong Mai, Xuefeng Zhao, Tianxiang Nan, Guozhong Xing and Songsong Zhang
Micromachines 2022, 13(12), 2250; https://doi.org/10.3390/mi13122250 - 17 Dec 2022
Cited by 4 | Viewed by 2079
Abstract
This paper presents a piezoresistive differential pressure sensor based on a silicon-on-insulator (SOI) structure for low pressure detection from 0 to 30 kPa. In the design phase, the stress distribution on the sensing membrane surface is simulated, and the doping concentration and geometry [...] Read more.
This paper presents a piezoresistive differential pressure sensor based on a silicon-on-insulator (SOI) structure for low pressure detection from 0 to 30 kPa. In the design phase, the stress distribution on the sensing membrane surface is simulated, and the doping concentration and geometry of the piezoresistor are evaluated. By optimizing the process, the realization of the pressure sensing diaphragm with a controllable thickness is achieved, and good ohmic contact is ensured. To obtain higher sensitivity and high temperature stability, an SOI structure with a 1.5 µm ultra-thin monocrystalline silicon layer is used in device manufacturing. The device diaphragm size is 700 µm × 700 µm × 2.1 µm. The experimental results show that the fabricated piezoresistive pressure sensor has a high sensitivity of 2.255 mV/V/kPa and a sensing resolution of less than 100 Pa at room temperature. The sensor has a temperature coefficient of sensitivity (TCS) of −0.221 %FS/°C and a temperature coefficient of offset (TCO) of −0.209 %FS/°C at operating temperatures ranging from 20 °C to 160 °C. The reported piezoresistive microelectromechanical systems (MEMS) pressure sensors are fabricated on 8-inch wafers using standard CMOS-compatible processes, which provides a volume solution for embedded integrated precision detection applications of air pressure, offering better insights for high-temperature and miniaturized low-pressure sensor research. Full article
(This article belongs to the Special Issue Design, Fabrication, Testing of MEMS/NEMS)
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13 pages, 4040 KiB  
Communication
A High-Sensitivity Bowel Sound Electronic Monitor Based on Piezoelectric Micromachined Ultrasonic Transducers
by Xiaoxia Ding, Zhipeng Wu, Mingze Gao, Minkan Chen, Jiawei Li, Tao Wu and Liang Lou
Micromachines 2022, 13(12), 2221; https://doi.org/10.3390/mi13122221 - 14 Dec 2022
Cited by 4 | Viewed by 2018
Abstract
Bowel sounds contain some important human physiological parameters which can reflect information about intestinal function. In this work, in order to realize real-time monitoring of bowel sounds, a portable and wearable bowel sound electronic monitor based on piezoelectric micromachined ultrasonic transducers (PMUTs) is [...] Read more.
Bowel sounds contain some important human physiological parameters which can reflect information about intestinal function. In this work, in order to realize real-time monitoring of bowel sounds, a portable and wearable bowel sound electronic monitor based on piezoelectric micromachined ultrasonic transducers (PMUTs) is proposed. This prototype consists of a sensing module to collect bowel sounds and a GUI (graphical user interface) based on LabVIEW to display real-time bowel sound signals. The sensing module is composed of four PMUTs connected in parallel and a signal conditioning circuit. The sensitivity, noise resolution, and non-linearity of the bowel sound monitor are measured in this work. The result indicates that the designed prototype has high sensitivity (−142.69 dB), high noise resolution (50 dB at 100 Hz), and small non-linearity. To demonstrate the characteristic of the designed electronic monitor, continuous bowel sound monitoring is performed using the electronic monitor and a stethoscope on a healthy human before and after a meal. Through comparing the experimental results and analyzing the signals in the time domain and frequency domain, this bowel sound monitor is demonstrated to record bowel sounds from the human intestine. This work displays the potential of the sensor for the daily monitoring of bowel sounds. Full article
(This article belongs to the Special Issue Design, Fabrication, Testing of MEMS/NEMS)
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16 pages, 4315 KiB  
Article
AlScN Film Based Piezoelectric Micromechanical Ultrasonic Transducer for an Extended Long-Range Detection
by Haolin Yang, Meilin Ji, Xueying Xiu, Haochen Lv, Alex Gu and Songsong Zhang
Micromachines 2022, 13(11), 1942; https://doi.org/10.3390/mi13111942 - 10 Nov 2022
Cited by 7 | Viewed by 2412
Abstract
Piezoelectric micromachined ultrasonic transducers (PMUTs) have been widely applied in distance sensing. However, the sensing distance of currently reported miniaturized ultrasonic sensors (e.g., PMUTs or CMUT) is still limited up to a certain range (e.g., ≤5 m) compared to conventional bulk ultrasonic devices. [...] Read more.
Piezoelectric micromachined ultrasonic transducers (PMUTs) have been widely applied in distance sensing. However, the sensing distance of currently reported miniaturized ultrasonic sensors (e.g., PMUTs or CMUT) is still limited up to a certain range (e.g., ≤5 m) compared to conventional bulk ultrasonic devices. This paper reports a PMUT array design using scandium-doped aluminum nitride (AlScN) as its piezoelectric layer for an extended long-range detection purpose. To minimize air attenuation, our device is resonating at 66 kHz for a high receive sensitivity of 5.7 mV/Pa. The proposed PMUT array can generate a sound pressure level (SPL) as high as 120 dB at a distance of 10 cm without beam forming. This PMUT design is catered for a pin-to-pin replacement of the current commercial bulk ultrasonic ranging sensor and works directly with the conventional range finding system (e.g., TI PGA460). In comparison with the common bulk transducer, the size of our device is 80% smaller. With the identical ranging detection setup, the proposed PMUT array improves the system SNR by more than 5 dB even at a distance as far as 6.8 m. The result of extended sensing distance validates our miniaturized PMUT array as the optimized candidate for most ultrasonic ranging applications. With the progressive development of piezoelectric MEMS, we believe that the PMUT technology could be a game changer in future long-range sensing applications. Full article
(This article belongs to the Special Issue Design, Fabrication, Testing of MEMS/NEMS)
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13 pages, 3599 KiB  
Article
Nondestructive Wafer Level MEMS Piezoelectric Device Thickness Detection
by Yongxin Zhou, Yuandong Gu and Songsong Zhang
Micromachines 2022, 13(11), 1916; https://doi.org/10.3390/mi13111916 - 05 Nov 2022
Viewed by 1541
Abstract
This paper introduces a novel nondestructive wafer scale thin film thickness measurement method by detecting the reflected picosecond ultrasonic wave transmitting between different interfacial layers. Unlike other traditional approaches used for thickness inspection, this method is highly efficient in wafer scale, and even [...] Read more.
This paper introduces a novel nondestructive wafer scale thin film thickness measurement method by detecting the reflected picosecond ultrasonic wave transmitting between different interfacial layers. Unlike other traditional approaches used for thickness inspection, this method is highly efficient in wafer scale, and even works for opaque material. As a demonstration, we took scandium doped aluminum nitride (AlScN) thin film and related piezoelectric stacking layers (e.g. Molybedenum/AlScN/Molybdenum) as the case study to explain the advantages of this approach. In our experiments, a laser with a wavelength of 515 nm was used to first measure the thickness of (1) a single Molybdenum (Mo) electrode layer in the range of 100–300 nm, and (2) a single AlScN piezoelectric layer in the range of 600–1000 nm. Then, (3) the combined stacking layers were measured. Finally, (4) the thickness of a standard piezoelectric composite structure (Mo/AlScN/Mo) was characterized based on the conclusions and derivation extracted from the aforementioned sets of experiments. This type of standard piezoelectric composite has been widely adopted in a variety of Micro-electromechanical systems (MEMS) devices such as the Piezoelectric Micromachined Ultrasonic Transducer (PMUT), the Film Bulk Acoustic Resonator (FBAR), the Surface Acoustic Wave (SAW) and more. A comparison between measurement data from both in-line and off-line (using Scanning Electron Microscope) methods was conducted. The result from such in situ 8-inch wafer scale measurements was in a good agreement with the SEM data. Full article
(This article belongs to the Special Issue Design, Fabrication, Testing of MEMS/NEMS)
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10 pages, 3864 KiB  
Article
Wide-Range Flexible Capacitive Pressure Sensors Based on Dielectrics with Various Porosity
by Huiyang Yu, Chengxi Guo, Xin Ye, Yifei Pan, Jiacheng Tu, Zhe Wu, Zefang Chen, Xueyang Liu, Jianqiu Huang, Qingying Ren and Yifeng Li
Micromachines 2022, 13(10), 1588; https://doi.org/10.3390/mi13101588 - 25 Sep 2022
Cited by 5 | Viewed by 1995
Abstract
Wide-range flexible pressure sensors are in difficulty in research while in demand in application. In this paper, a wide-range capacitive flexible pressure sensor is developed with the foaming agent ammonium bicarbonate (NH4HCO3). By controlling the concentration of NH4 [...] Read more.
Wide-range flexible pressure sensors are in difficulty in research while in demand in application. In this paper, a wide-range capacitive flexible pressure sensor is developed with the foaming agent ammonium bicarbonate (NH4HCO3). By controlling the concentration of NH4HCO3 doped in the polydimethylsiloxane (PDMS) and repeating the curing process, pressure-sensitive dielectrics with various porosity are fabricated to expand the detection range of the capacitive pressure sensor. The shape and the size of each dielectric is defined by the 3D printed mold. To improve the dielectric property of the dielectric, a 1% weight ratio of multi-walled carbon nanotubes (MWCNTs) are doped into PDMS liquid. Besides that, a 5% weight ratio of MWCNTs is dispersed into deionized water and then coated on the electrodes to improve the contact state between copper electrodes and the dielectric. The laminated dielectric layer and two electrodes are assembled and tested. In order to verify the effectiveness of this design, some reference devices are prepared, such as sensors based on the dielectric with uniform porosity and a sensor with common copper electrodes. According to the testing results of these sensors, it can be seen that the sensor based on the dielectric with various porosity has higher sensitivity and a wider pressure detection range, which can detect the pressure range from 0 kPa to 1200 kPa and is extended to 300 kPa compared with the dielectric with uniform porosity. Finally, the sensor is applied to the fingerprint, finger joint, and knee bending test. The results show that the sensor has the potential to be applied to human motion detection. Full article
(This article belongs to the Special Issue Design, Fabrication, Testing of MEMS/NEMS)
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19 pages, 5965 KiB  
Article
Development of MEMS Process Compatible (Bi,Sb)2(Se,Te)3-Based Thin Films for Scalable Fabrication of Planar Micro-Thermoelectric Generators
by Prithu Bhatnagar and Daryoosh Vashaee
Micromachines 2022, 13(9), 1459; https://doi.org/10.3390/mi13091459 - 02 Sep 2022
Cited by 4 | Viewed by 1851
Abstract
Bismuth telluride-based thin films have been investigated as the active material in flexible and micro thermoelectric generators (TEGs) for near room-temperature energy harvesting applications. The latter is a class of compact printed circuit board compatible devices conceptualized for operation at low-temperature gradients to [...] Read more.
Bismuth telluride-based thin films have been investigated as the active material in flexible and micro thermoelectric generators (TEGs) for near room-temperature energy harvesting applications. The latter is a class of compact printed circuit board compatible devices conceptualized for operation at low-temperature gradients to generate power for wireless sensor nodes (WSNs), the fundamental units of the Internet-of-Things (IoT). CMOS and MEMS compatible micro-TEGs require thin films that can be integrated into the fabrication flow without compromising their thermoelectric properties. We present results on the thermoelectric properties of (Bi,Sb)2(Se,Te)3 thin films deposited via thermal evaporation of ternary compound pellets on four-inch SiO2 substrates at room temperature. Thin-film compositions and post-deposition annealing parameters are optimized to achieve power factors of 2.75 mW m−1 K−2 and 0.59 mW m−1 K−2 for p-type and n-type thin films. The measurement setup is optimized to characterize the thin-film properties accurately. Thin-film adhesion is further tested and optimized on several substrates. Successful lift-off of p-type and n-type thin films is completed on the same wafer to create thermocouple patterns as per the target device design proving compatibility with the standard MEMS fabrication process. Full article
(This article belongs to the Special Issue Design, Fabrication, Testing of MEMS/NEMS)
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16 pages, 5193 KiB  
Article
Design and Fabrication of Millimeter-Wave Frequency-Tunable Metamaterial Absorber Using MEMS Cantilever Actuators
by Myungjin Chung, Heijun Jeong, Yong-Kweon Kim, Sungjoon Lim and Chang-Wook Baek
Micromachines 2022, 13(8), 1354; https://doi.org/10.3390/mi13081354 - 20 Aug 2022
Cited by 7 | Viewed by 2094
Abstract
In this paper, a MEMS (Micro Electro Mechanical Systems)-based frequency-tunable metamaterial absorber for millimeter-wave application was demonstrated. To achieve the resonant-frequency tunability of the absorber, the unit cell of the proposed metamaterial was designed to be a symmetric split-ring resonator with a stress-induced [...] Read more.
In this paper, a MEMS (Micro Electro Mechanical Systems)-based frequency-tunable metamaterial absorber for millimeter-wave application was demonstrated. To achieve the resonant-frequency tunability of the absorber, the unit cell of the proposed metamaterial was designed to be a symmetric split-ring resonator with a stress-induced MEMS cantilever array having initial out-of-plane deflections, and the cantilevers were electrostatically actuated to generate a capacitance change. The dimensional parameters of the absorber were determined via impedance matching using a full electromagnetic simulation. The designed absorber was fabricated on a glass wafer with surface micromachining processes using a photoresist sacrificial layer and the oxygen-plasma-ashing process to release the cantilevers. The performance of the fabricated absorber was experimentally validated using a waveguide measurement setup. The absorption frequency shifted down according to the applied DC (direct current) bias voltage from 28 GHz in the initial off state to 25.5 GHz in the pull-down state with the applied voltage of 15 V. The measured reflection coefficients at those frequencies were −5.68 dB and −33.60 dB, corresponding to the peak absorptivity rates of 72.9 and 99.9%, respectively. Full article
(This article belongs to the Special Issue Design, Fabrication, Testing of MEMS/NEMS)
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20 pages, 4593 KiB  
Article
A Novel Design Nomogram for Optimization of Micro Search Coil Magnetometer for Energy Monitoring in Smart Buildings
by Hadi Tavakkoli, Kui Song, Xu Zhao, Mingzheng Duan and Yi-Kuen Lee
Micromachines 2022, 13(8), 1342; https://doi.org/10.3390/mi13081342 - 18 Aug 2022
Cited by 4 | Viewed by 1363
Abstract
In this paper, a new analytical method to achieve the maximum signal-to-noise ratio (SNR) of a micro search coil magnetometer (µSCM) is presented. A planar spiral inductor was utilized to miniaturize conventional bulky search coil magnetometers. First, dimensional analysis was applied [...] Read more.
In this paper, a new analytical method to achieve the maximum signal-to-noise ratio (SNR) of a micro search coil magnetometer (µSCM) is presented. A planar spiral inductor was utilized to miniaturize conventional bulky search coil magnetometers. First, dimensional analysis was applied to identify three dimensionless parameters for the µSCM’s key performance indices (sensitivity (Se), noise, and SNR). The effect of the parameters on the µSCM’s performance was carefully investigated, and a novel 4D nomogram was developed. Furthermore, an SNR analysis considering noise sources of a low-noise amplifier was performed. By combining the results from the nomogram and the effect of the noise sources from the amplifier circuit, optimum values for the dimensionless parameters were calculated. According to the calculation results, the dominant noise source varied with an increase in the track width ratio to the outer diameter. Seven different samples were fabricated by a single-mask lithography process. The sensitivity of 1612 mV/mT was demonstrated at a 50 Hz input magnetic field, which was better than the previous µSCM (Se = 6.5 mV/mT) by more than 2 orders of magnitude. Finally, one of the fabricated µSCMs was employed to measure the online power consumption of a personal computer while different types of software were running. Full article
(This article belongs to the Special Issue Design, Fabrication, Testing of MEMS/NEMS)
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18 pages, 9007 KiB  
Article
Structural Design and Testing of a Micromechanical Resonant Accelerometer
by Heng Liu, Yu Zhang and Jiale Wu
Micromachines 2022, 13(8), 1271; https://doi.org/10.3390/mi13081271 - 07 Aug 2022
Cited by 2 | Viewed by 1436
Abstract
Micromechanical resonant accelerometers based on electrostatic stiffness have the advantage of it being possible to adjust their sensitivity by changing the detection voltage. However, there is a high-order nonlinear relationship between the output frequency and the induced acceleration, so it is difficult to [...] Read more.
Micromechanical resonant accelerometers based on electrostatic stiffness have the advantage of it being possible to adjust their sensitivity by changing the detection voltage. However, there is a high-order nonlinear relationship between the output frequency and the induced acceleration, so it is difficult to obtain the theoretical basis to guide the microstructure design. In this study, the dynamic equation for this type of accelerometer was established under the condition of the stiffness of the folded beams being much less than that of the resonant beams. The sensitivity was obtained first, and then silicon-based microstructures were fabricated, for which metal tube-shell vacuum packaging was adopted. The two static driving capacitances were about 0.88 pF, and the detection capacitances were about 0.38 pF in the experimental test. The sensitivity was 44.5 Hz/g when the detection voltage was 1 V, while it was greater than 300 Hz/g when the detection voltage was 3 V. With an increase in the detection and driving voltages, a coupling phenomenon occurred between the vibration amplitude and frequency of the resonant beam. The double-stage folded beam failed at a high detection voltage larger than 10 V. Through the experiment, a numerical simulation model for the accelerometer was established, providing the basis for a closed-loop control circuit design. Full article
(This article belongs to the Special Issue Design, Fabrication, Testing of MEMS/NEMS)
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13 pages, 4757 KiB  
Article
High Quality-Factor and Spectrum-Clean AlN Lamb-Wave Resonators with Optimized Lateral Reflection Boundary Conditions and Transducer Design
by Haiyan Sun, Shitao Lv, Aoyu Zhang, Chenguang Song, Xinyi Sun, Fazeng Tan, Liuhong Liang, Yinfang Zhu and Jicong Zhao
Micromachines 2022, 13(5), 779; https://doi.org/10.3390/mi13050779 - 15 May 2022
Cited by 4 | Viewed by 1940
Abstract
This paper presents a high quality-factor (Q) and spectrum-clean AlN Lamb-wave resonator (LWR). The width of its lateral reflection boundary was optimized to weaken the transverse modes’ coupling and wave guiding, and then to improve the LWR’s Q value and spectral [...] Read more.
This paper presents a high quality-factor (Q) and spectrum-clean AlN Lamb-wave resonator (LWR). The width of its lateral reflection boundary was optimized to weaken the transverse modes’ coupling and wave guiding, and then to improve the LWR’s Q value and spectral purity, which was verified by finite element analysis and experimental characterization. In addition, the series resonance quality factor (Qs) value of the interdigitated (IDT)-Ground LWR is similar to that of the IDT-Floating LWR, but its parallel resonance quality factor (Qp) is nearly doubled, due to the reduction of the electrical loss induced by its static capacitance (C0). The measured results show that the designed LWR with optimized boundary reflection conditions and IDT-Ground structure exhibit Qs and Qp values as high as 4019.8 and 839.5 at 401.2 MHz and 402.9 MHz, respectively, meanwhile, it has good spectral purity. Moreover, the influence of the metal ratio and material of the LWR’s IDT electrodes on the device’s performance was also studied by theoretical analysis and experimental verification. Full article
(This article belongs to the Special Issue Design, Fabrication, Testing of MEMS/NEMS)
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