Any device which senses information such as shape, texture, softness, temperature, vibration or shear and normal forces, by physical contact or touch, can be termed a tactile sensor. The importance of tactile sensor technology was recognized in the 1980s, along with a realization of the importance of computers and robotics. Despite this awareness, tactile sensors failed to be strongly adopted in industrial or consumer markets. In this paper, previous expectations of tactile sensors have been reviewed and the reasons for their failure to meet these expectations are discussed. The evolution of different tactile transduction principles, state of art designs and fabrication methods, and their pros and cons, are analyzed. From current development trends, new application areas for tactile sensors have been proposed. Literature from the last few decades has been revisited, and areas which are not appropriate for the use of tactile sensors have been identified. Similarly, the challenges that this technology needs to overcome in order to find its place in the market have been highlighted.

/pdf/a-review-of-tactile-sensing-technologies-with-applications-12ul5smpoy.pdf

A review of tactile sensing technologies with applications in biomedical engineering

The majority of microelectromechanical system (MEMS) devices must be combined with integrated circuits (ICs) for operation in larger electronic systems. While MEMS transducers sense or control phys ...

/pdf/integrating-mems-and-ics-3tx6wanytd.pdf

Integrating MEMS and ICs

During the last decades, smart tactile sensing systems based on different sensing techniques have been developed due to their high potential in industry and biomedical engineering. However, smart tactile sensing technologies and systems are still in their infancy, as many technological and system issues remain unresolved and require strong interdisciplinary efforts to address them. This paper provides an overview of smart tactile sensing systems, with a focus on signal processing technologies used to interpret the measured information from tactile sensors and/or sensors for other sensory modalities. The tactile sensing transduction and principles, fabrication and structures are also discussed with their merits and demerits. Finally, the challenges that tactile sensing technology needs to overcome are highlighted.

https://www.mdpi.com/1424-8220/17/11/2653/pdf

Novel Tactile Sensor Technology and Smart Tactile Sensing Systems: A Review.

The majority of microelectromechanical system (MEMS) devices must be combined with integrated circuits (ICs) for operation in larger electronic systems. While MEMS transducers sense or control physical, optical or chemical quantities, ICs typically provide functionalities related to the signals of these transducers, such as analog-to-digital conversion, amplification, filtering and information processing as well as communication between the MEMS transducer and the outside world. Thus, the vast majority of commercial MEMS products, such as accelerometers, gyroscopes and micro-mirror arrays, are integrated and packaged together with ICs. There are a variety of possible methods of integrating and packaging MEMS and IC components, and the technology of choice strongly depends on the device, the field of application and the commercial requirements. In this review paper, traditional as well as innovative and emerging approaches to MEMS and IC integration are reviewed. These include approaches based on the hybrid integration of multiple chips (multi-chip solutions) as well as system-on-chip solutions based on wafer-level monolithic integration and heterogeneous integration techniques. These are important technological building blocks for the More-Than-Moore paradigm described in the International Technology Roadmap for Semiconductors. In this paper, the various approaches are categorized in a coherent manner, their merits are discussed, and suitable application areas and implementations are critically investigated. The implications of the different MEMS and IC integration approaches for packaging, testing and final system costs are reviewed.

/pdf/integrating-mems-and-ics-5evxuk7ch7.pdf

Tactile sensors for robotic applications

This paper describes a low power, low phase noise 5.8 GHz voltage controlled oscillator (VCO) with on-chip CMOS MEMS inductor. The inductor was fabricated by TSMC 0.18 μm one-poly six-metal (1P6M) CMOS process and also Chip Implementation Center (CIC) micromachining post-process. During the post-process, the dry etching was utilized to remove the oxide between the winding metals and the silicon substrate under the inductor. Due to the alleviation of parasitic capacitance and lossy substrate, the quality factor and resonant frequency will be improved and extended. In this work, quality factor up to 15 was obtained for a 1.88 nH micromachined inductor at 8.5 GHz, and the improvement is up to 88% in maximum quality factor. The CMOS and micromachined inductor were both implemented with a 5.8 GHz VCO. Compared side by side with the CMOS inductor, the CMOS MEMS inductor produced a 5 dB lower phase noise improvement at 1 MHz offset in this 5.8 GHz VCO.

/pdf/a-5-8-ghz-vco-with-cmos-compatible-mems-inductors-1h2jnwbee3.pdf

A 5.8-GHz VCO with CMOS-compatible MEMS inductors

This paper describes the design and characterization of a CMOS-micromachined tactile sensing device that can be utilized for fingerprint recognition. The complete post micromachining steps are performed at die level without resorting to a wafer-level process, providing a low-cost solution for production. The micromechanical structure has an area of 200 mum by 200 mum and an initial sensing capacitance of 153 fF. An oscillator circuit is used to convert the pressure induced capacitance change to a shift in output frequency. The circuit has a measured initial frequency at 49.5 MHz under no applied force. The total frequency shift is 14 MHz with a corresponding mechanical displacement of 0.56 mum and a capacitance change of 63 fF, averaging a capacitive sensitivity of 222 kHz/fF. The measured spring constant is 923N/m, producing a force sensitivity of 27.1 kHz/muN

A CMOS Micromachined Capacitive Tactile Sensor With High-Frequency Output

This paper describes the design, fabrication and characterization of a complementary metal-oxide-semiconductor (CMOS) micro-electro-mechanical-system (MEMS) accelerometer implemented in a 0.18 µm multi-project wafer (MPW) CMOS MEMS process. In addition to the standard CMOS process, an additional aluminum layer and a thick photoresist masking layer are employed to achieve etching and microstructural release. The structural thickness of the accelerometer is up to 9 µm and the minimum structural spacing is 2.3 µm. The out-of-plane deflection resulted from the vertical stress gradient over the whole device is controlled to be under 0.2 µm. The chip area containing the micromechanical structure and switched-capacitor sensing circuit is 1.18 × 0.9 mm2, and the total power consumption is only 0.7 mW. Within the sensing range of ±6 G, the measured nonlinearity is 1.07% and the cross-axis sensitivities with respect to the in-plane and out-of-plane are 0.5% and 5.8%, respectively. The average sensitivity of five tested accelerometers is 191.4 mV G−1with a standard deviation of 2.5 mV G−1. The measured output noise floor is 354 µG Hz−1/2, corresponding to a 100 Hz 1 G sinusoidal acceleration. The measured output offset voltage is about 100 mV at 27 °C, and the zero-G temperature coefficient of the accelerometer output is 0.94 mV °C−1 below 85 °C.

http://iopscience.iop.org/article/10.1088/0960-1317/22/5/055010/pdf

Implementation of a monolithic capacitive accelerometer in a wafer-level 0.18 µm CMOS MEMS process

This paper describes the design and characterization of a capacitive tactile sensor fabricated in a conventional CMOS process. To achieve a high capacitive sensitivity, an oscillator circuit is adopted to convert the pressure induced capacitive change to an output frequency shift. The complete post micromachining steps are performed on a CMOS die without resorting to a wafer process. The pressure-sensing membrane has a total size of 200 µ m × 200 µ m with an initial sensing capacitance of 153 fF. Experimental results show an initial frequency output at 48.96 MHz under no applied load. The total frequency shift is 13.5 MHz with a corresponding membrane displacement of 0.56 µ m and a capacitance change of 63 fF, averaging 0.21 MHz/fF. The measured force sensitivity is 26.1 kHz/µ N.

/pdf/a-highly-sensitive-cmos-mems-capacitive-tactile-sensor-dq8ccdzz87.pdf

A Highly Sensitive CMOS-MEMS Capacitive Tactile Sensor

This work describes the design and characterization of integrated CMOS (complementary metal oxide semiconductor) oscillators comprising a capacitively transduced micromechanical resonator and a phase-locked loop (PLL) driving circuit. Three oscillator schemes are studied and compared, including direct feedback, direct feedback containing a PLL and hybrid direct feedback plus a PLL. PLL is known for its capability in automatic tuning and tracking of a reference signal. Inclusion of a PLL is beneficial for sustaining oscillations at resonant frequencies within its capture range. The micromechanical resonator has a measured resonant frequency of 117.3 kHz. The CMOS PLL circuit has a closed-loop bandwidth of 1.8 kHz with a capture range between 111 kHz and 118.4 kHz. The start-up times for oscillation are shortened in the two schemes utilizing a PLL, since it provides an initial driving signal at its free-running frequency. The lock-in time is also reduced by increasing the proportion of PLL drive in the hybrid scheme. The measured noises for the three oscillator schemes are similar with a value of −75 dB below the resonant peak at a 10 Hz offset.

https://iopscience.iop.org/article/10.1088/0960-1317/22/5/055024/pdf

Sheng-Hsiang Tseng

Papers

A 5.8-GHz VCO with CMOS-compatible MEMS inductors

A CMOS Micromachined Capacitive Tactile Sensor With High-Frequency Output

Implementation of a monolithic capacitive accelerometer in a wafer-level 0.18 µm CMOS MEMS process

A Highly Sensitive CMOS-MEMS Capacitive Tactile Sensor

Study of CMOS micromachined self-oscillating loop utilizing a phase-locked loop-driving circuit