POSFET tactile sensing arrays using CMOS technology

This work presents fabrication and evaluation of novel POSFET (Piezoelectric Oxide Semiconductor Field Effect Transistor) devices based tactile sensing chip. In the newer version presented here, the tactile sensing chip has been fabricated using CMOS (Complementary Metal Oxide Semiconductor) technology. The chip consists of 4 x 4 POSFET touch sensing devices (or taxels) and both, the individual taxels and the array are designed to match spatio–temporal performance of the human fingertips. To detect contact events, the taxels utilize the contact forces induced change in the polarization level of piezoelectric polymer (and hence change in the induced channel current of MOS). The POSFET device on the chip have linear response in the tested dynamic contact forces range of 0.01–3 N and the sensitivity (without amplification) is 102.4 mV/N

Tactile sensing chips with POSFET array and integrated interface electronics

This work presents the advanced version of novel POSFET (Piezoelectric Oxide Semiconductor Field Effect Transistor) devices based tactile sensing chip. The new version of the tactile sensing chip presented here comprises of a 4 x 4 array of POSFET touch sensing devices and integrated interface electronics (i.e. multiplexers, high compliance current sinks and voltage output buffers). The chip also includes four temperature diodes for the measurement of contact temperature. Various components on the chip have been characterized systematically and the overall operation of the tactile sensing system has been evaluated. With new design the POSFET devices have improved performance (i.e. linear response in the dynamic contact forces range of 0.01–3N and sensitivity (without amplification) of 102.4 mV/N), which is more than twice the performance of their previous implementations. The integrated interface electronics result in reduced interconnections which otherwise would be needed to connect the POSFET array with off-chip interface electronic circuitry. This research paves the way for CMOS (Complementary Metal Oxide Semiconductor) implementation of full on-chip tactile sensing systems based on POSFETs

Device modelling for bendable piezoelectric FET-based touch sensing system

Flexible electronics is rapidly evolving towards devices and circuits to enable numerous new applications. The high-performance, in terms of response speed, uniformity and reliability, remains a sticking point. The potential solutions for high-performance related challenges bring us back to the timetested silicon based electronics. However, the changes in the response of silicon based devices due to bending related stresses is a concern, especially because there are no suitable models to predict this behavior. This also makes the circuit design a difficult task. This paper reports advances in this direction, through our research on bendable Piezoelectric Oxide Semiconductor Field Effect Transistor (POSFET) based touch sensors. The analytical model of POSFET, complimented with Verilog-A model, is presented to describe the device behavior under normal force in planar and stressed conditions. Further, dynamic readout circuit compensation of POSFET devices have been analyzed and compared with similar arrangement to reduce the piezoresistive effect under tensile and compressive stresses. This approach introduces a first step towards the systematic modeling of stress induced changes in device response. This systematic study will help realize high-performance bendable microsystems with integrated sensors and readout circuitry on ultra-thin chips (UTCs) needed in various applications, in particular, the electronic skin (e-skin)

Large Area Electronic Skin

Technological advances have enabled various approaches for developing artificial organs such as bionic eyes, artificial ears, and lungs etc. Recently electronics (e-skin) or tactile skin has attracted increasing attention for its potential to detect subtle pressure changes, which may open up applications including real-time health monitoring, minimally invasive surgery, and prosthetics. The development of e-skin is challenging as, unlike other artificial organs, tactile skin has large number of different types of sensors, which are distributed over large areas and generate large amount of data. On top of this, the attributes such as softness, stretchability, and bendability etc., are difficult to be achieved as today's electronics technology is meant for electronics on planar and stiff substrates such as silicon wafers. This said, many advances, pursued through “More than Moore” technology, have recently raised hope as some of these relate to flexible electronics and have been targeted towards developing e-skin. Depending on the technology and application, the scale of e-skin could vary from small patch (e.g. for health monitoring) to large area skin (e.g. for robotics). This invited paper presents some of the advances in large area e-skin and flexible electronics, particularly related to robotics

Multiple facets of tightly coupled transducer-transistor structures

The ever increasing demand for data processing requires different paradigms for electronics. Excellent performance capabilities such as low power and high speed in electronics can be attained through several factors including using functional materials, which sometimes acquire superior electronic properties. The transduction-based transistor switching mechanism is one such possibility, which exploits the change in electrical properties of the transducer as a function of a mechanically induced deformation. Originally developed for deformation sensors, the technique is now moving to the centre stage of the electronic industry as the basis for new transistor concepts to circumvent the gate voltage bottleneck in transistor miniaturization. In issue 37 of Nanotechnology, Chang et al show the piezoelectronic transistor (PET), which uses a fast, low-power mechanical transduction mechanism to propagate an input gate voltage signal into an output resistance modulation. The findings by Chang et al will spur further research into piezoelectric scaling, and the PET fabrication techniques needed to advance this type of device in the future

Device Modelling of Silicon Based High-Performance Flexible Electronics

The area of flexible electronics is rapidly expanding and evolving. With applications requiring high speed and performance, ultra-thin silicon-based electronics has shown its prominence. However, the change in device response upon bending is a major concern. In absence of suitable analytical and design tool friendly model, the behavior under bent condition is hard to predict. This poses challenges to circuit designer working in the bendable electronics field, in laying out a design that can give a precise response in a stressed condition. This paper presents advances in this direction and investigates the effect of compressive and tensile stress on the performance of NMOS and PMOS transistor and a touch sensor comprising a transistor and piezoelectric capacitor

Ultra-thin silicon based piezoelectric capacitive tactile sensor

This paper presents an ultra-thin bendable silicon based tactile sensor, in a piezoelectric capacitor configuration, realized by wet anisotropic etching as post-processing steps. The device is fabricated over bulk silicon, which is thinned down to 35 μm from an original thickness of 636 μm. Dicing of thin membrane is achieved by low cost novel technique of Dicing before Etching. The piezoelectric capacitor is composed of polyvinylidene fluoride trifluoroethylene (PVDF-TrFE), which present an attractive avenue for tactile sensing as they respond to dynamic contact events (which is critical for robotic tasks), easy to fabricate at low cost and are inherently flexible. The sensor exhibits enhanced piezoelectric properties, thanks to the optimization of the poling procedure. The sensor capacitive behaviour is confirmed using impedance analysis and the electro-mechanical characterization is done using TIRA shaker setup

Event Driven Tactile Sensors for Artificial Devices

Present-day robots are, to some extent, able to deal with high complexity and variability of the real-world environment. Their cognitive capabilities can be further enhanced, if they physically interact and explore the real-world objects. For this, the need for efficient tactile sensors is growing day after day in such a way are becoming more and more part of daily life devices especially in robotic applications for manipulation and safe interaction with the environment. In this thesis, we highlight the importance of touch sensing in humans and robots. Inspired by the biological systems, in the the first part, we merge between neuromorphic engineering and CMOS technology where the former is a eld of science that replicates what is biologically (neurons of the nervous system) inside humans into the circuit level. We explain the operation and then characterize different sensor circuits through simulation and experiment to propose finally new prototypes based on the achieved results. In the second part, we present a machine learning technique for detecting the direction and orientation of a sliding tip over a complete skin patch of the iCub robot. Through learning and online testing, the algorithm classies different trajectories across the skin patch. Through this part, we show the results of the considered algorithm with a future perspective to extend the work

A spiking and adapting tactile sensor for neuromorphic applications

The ongoing research on and development of increasingly intelligent artificial systems propels the need for bio inspired pressure sensitive spiking circuits. Here we present an adapting and spiking tactile sensor, based on a neuronal model and a piezoelectric field-effect transistor (PiezoFET). The piezoelectric sensor device consists of a metal-oxide semiconductor field-effect transistor comprising a piezoelectric aluminium-scandium-nitride (AlxSc1-xN) layer inside of the gate stack. The so augmented device is sensitive to mechanical stress. In combination with an analogue circuit, this sensor unit is capable of encoding the mechanical quantity into a series of spikes with an ongoing adaptation of the output frequency. This allows for a broad application in the context of robotic and neuromorphic systems, since it enables said systems to receive information from the surrounding environment and provide encoded spike trains for neuromorphic hardware. We present numerical and experimental results on this spiking and adapting tactile sensor