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)

Giant Magnetoresistive Biosensors for Time-Domain Magnetorelaxometry: A Theoretical Investigation and Progress Toward an Immunoassay.

Magnetorelaxometry (MRX) is a promising new biosensing technique for point-of-care diagnostics. Historically, magnetic sensors have been primarily used to monitor the stray field of magnetic nanoparticles bound to analytes of interest for immunoassays and flow cytometers. In MRX, the magnetic nanoparticles (MNPs) are first magnetized and then the temporal response is monitored after removing the magnetic field. This new sensing modality is insensitive to the magnetic field homogeneity making it more amenable to low-power portable applications. In this work, we systematically investigated time-domain MRX by measuring the signal dependence on the applied field, magnetization time, and magnetic core size. The extracted characteristic times varied for different magnetic MNPs, exhibiting unique magnetic signatures. We also measured the signal contribution based on the MNP location and correlated the coverage with measured signal amplitude. Lastly, we demonstrated, for the first time, a GMR-based time-domain MRX bioassay. This approach validates the feasibility of immunoassays using GMR-based MRX and provides an alternative platform for point-of-care diagnostics

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

Modelling of Spintronic Nanodevices for Neuromorphic Sensing Chips

No abstract available

Spintronic Nanodevices for Neuromorphic Sensing Chips

Recent developments in spintronics materials and physics are promising to develop a new type of magnetic sensors which can be embedded into the silicon chips. These neuromorphic sensing chips will be designed to capture the biomagnetic signals from active biological tissue exploited as brain-machine interface. They lead to machines that are able to sense and interact with the world in humanlike ways and able to accelerate years of fitful advance in artificial intelligence. To detect the weak biomagnetic signals, this work aims to develop a CMOS-compatible spintronic sensor based on the magnetoresistive (MR) effect. As an alternative to bulky superconducting quantum interference device (SQUID) systems, the miniaturised spintronic devices can be integrated with standard CMOS technologies makes it possible to detect weak biomagnetic signals with micron-sized, non-cooled and low-cost. Fig. 1 shows the finite element method (FEM)-based simulation results of a Tunnelling-Magnetoresistive (TMR) sensor with an optimal structure in COMSOL Multiphysics. The finest geometry and material are demonstrated and compared with the state-of-the-art. The proposed TMR sensor achieves a linear response with a high TMR ratio of 172% and sensitivity of 223 μV/Oe. The results are promising for utilizing the TMR sensors in future miniaturized brain-machine interface, such as Magnetoencephalography (MEG) systems for neuromorphic sensing

An Extended CMOS ISFET Model Incorporating the Physical Design Geometry and the Effects on Performance and Offset Variation

This paper presents an extended model for the CMOS-based ion-sensitive field-effect transistor, incorporating design parameters associated with the physical geometry of the device. This can, for the first time, provide a good match between calculated and measured characteristics by taking into account the effects of nonidealities such as threshold voltage variation and sensor noise. The model is evaluated through a number of devices with varying design parameters (chemical sensing area and MOSFET dimensions) fabricated in a commercially available 0.35-µm CMOS technology. Threshold voltage, subthreshold slope, chemical sensitivity, drift, and noise were measured and compared with the simulated results. The first- and second-order effects are analyzed in detail, and it is shown that the sensors' performance was in agreement with the proposed model

Device modelling of MgO-barrier tunnelling magnetoresistors for hybrid spintronic-CMOS

Spintronic sensors, that are based on the tunnellingmagnetoresistive (TMR) effect, have been utilized in detecting low magnetic fields. However, still no computer-based model of these devices is available to integrated circuit designer to implement them in a hybrid spintronic-CMOS system. We developed a finite element method (FEM)-based model of a MgO-barrier TMR device in COMSOL Multiphysics®. The parameters of this model were extracted from the state-of-the-art fabrication and experimental data. Results were compared with respect to the model geometry and the used material. The proposed TMR sensor model offers a linear response with a high TMR ratio of 233% at 10 mV power supply. The model was exported to Cadence© Spectre to create a compact model using Verilog-A language. The developed sensor model was simulated with its analog front-end in same environment. This model provided a reliable benchmark for modelling of the future hybrid spintronic-CMOS developments