This paper provides a review on some of the significant research work done on wearable flexible sensors (WFSs). Sensors fabricated with the flexible materials have been attached to a person along with the embedded system to monitor a parameter and transfer the significant data to the monitoring unit for the further analyses. The use of wearable sensors has played a quite important role to monitor the physiological parameters of a person to minimize any malfunctioning happening in the body. This paper categorizes the work according to the materials used for designing the system, the network protocols, and different types of activities that were being monitored. The challenges faced by the current sensing systems and future opportunities for the WFSs regarding its market values are also briefly explained in this paper.

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Wearable Flexible Sensors: A Review

The state-of-the-art in wearable flexible sensors (WFSs) for sweat analyte detection was investigated. Recent advances show the development of integrated, mechanically flexible and multiplexed sens...

https://royalsocietypublishing.org/doi/pdf/10.1098/rsif.2019.0217

Wearable flexible sweat sensors for healthcare monitoring: a review.

The ATLAS Collaboration will upgrade its semiconductor pixel tracking detector with a new Insertable B-layer (IBL) between the existing pixel detector and the vacuum pipe of the Large Hadron Collider. The extreme operating conditions at this location have necessitated the development of new radiation hard pixel sensor technologies and a new front-end readout chip, called the FE-I4. Planar pixel sensors and 3D pixel sensors have been investigated to equip this new pixel layer, and prototype modules using the FE-I4A have been fabricated and characterized using 120 GeV pions at the CERN SPS and 4 GeV positrons at DESY, before and after module irradiation. Beam test results are presented, including charge collection efficiency, tracking efficiency and charge sharing.

/pdf/prototype-atlas-ibl-modules-using-the-fe-i4a-front-end-48na0b6a29.pdf

Prototype ATLAS IBL modules using the FE-I4A front-end readout chip

We propose to develop a fast, thin silicon sensor with gain capable to concurrently measure with high precision the space (∼10 μm) and time (∼10 ps) coordinates of a particle. This will open up new application of silicon detector systems in many fields. Our analysis of detector properties indicates that it is possible to improve the timing characteristics of silicon-based tracking sensors, which already have sufficient position resolution, to achieve four-dimensional high-precision measurements. The basic sensor characteristics and the expected performance are listed, the wide field of applications are mentioned and the required R&D topics are discussed.

Ultra-fast silicon detectors

We have been developing a novel radiation-tolerant n+-in-p silicon microstrip sensor for very high radiation environments, aiming for application in the high luminosity large hadron collider. The sensors are fabricated in 6 in., p-type, float-zone wafers, where large-area strip sensor designs are laid out together with a number of miniature sensors. Radiation tolerance has been studied with ATLAS07 sensors and with independent structures. The ATLAS07 design was developed into new ATLAS12 designs. The ATLAS12A large-area sensor is made towards an axial strip sensor and the ATLAS12M towards a stereo strip sensor. New features to the ATLAS12 sensors are two dicing lines: standard edge space of 910 μm and slim edge space of 450 μm, a gated punch-through protection structure, and connection of orphan strips in a triangular corner of stereo strips. We report the design of the ATLAS12 layouts and initial measurements of the leakage current after dicing and the resistivity of the wafers.

/pdf/development-of-n-in-p-large-area-silicon-microstrip-sensors-2ud32s38az.pdf

Development of n + -in-p large-area silicon microstrip sensors for very high radiation environments - ATLAS12 design and initial results

We have developed a novel and highly radiation-tolerant n-in-p silicon microstrip sensor for very high radiation environments such as in the Super Large Hadron Collider. The sensors are designed for a fluence of 1×1015 neq/cm2 and are fabricated from p-type, FZ, 6 in. (150 mm) wafers onto which we lay out a single 9.75 cm×9.75 cm large-area sensor and several 1 cm×1 cm miniature sensors with various n-strip isolation structures. By evaluating the sensors both pre- and post-irradiation by protons and neutrons, we find that the full depletion voltage evolves to approximately 800 V and that the n-strip isolation depends on the p+ concentration. In addition, we characterize the interstrip resistance, interstrip capacitance and the punch-through-protection (PTP) voltage. The first fabrication batch allowed us to identify the weak spots in the PTP and the stereo strip layouts. By understanding the source of the weakness, the mask was modified accordingly. After modification, the follow-up fabrication batches and the latest fabrication of about 30 main sensors and associated miniature sensors have shown good performance, with no sign of microdischarge up to 1000 V.

Development of n-on-p silicon sensors for very high radiation environments

Both the collected charge and the capacitance of a silicon detector are proportional to the depleted depth of the space charge region. The presence of deep levels introduces frequency dependence in the measured capacitance, and this frequency dependence can be corrected for by analyzing the data using admittance spectroscopy. An equivalent circuit for a PN junction containing deep levels is used to accurately model deep level response. Activation energy, majority carrier cross-section and the concentration of active deep levels at the edge of the space charge region is determined. Space charge region depth as a function of the applied voltage is extracted for various detectors irradiated with neutrons and pions. When possible, depleted depths are compared to charge collection measurements.

/pdf/analysis-of-deep-level-parameters-in-irradiated-silicon-4t2r3o9itm.pdf

Analysis of deep level parameters in irradiated silicon detectors

The depletion depth of silicon strip detectors can be inferred from both the reciprocal capacitance and from the amount of collected charge. In addition, the depth profile of the doping density and the electric field has been inferred from charge collection (generated by laser light or charged particles). We show that the depth profile of the space charge can be derived from Capacitance-Voltage (C-V) measurements using continuity constraints on the potential, field and leakage current. We analyze both un-irradiated and irradiated p-type strip sensors, show that a double-junction structure can be derived with space charge distribution depending on the bias voltage.

M. Gerling

Papers

Development of n-on-p silicon sensors for very high radiation environments

Analysis of deep level parameters in irradiated silicon detectors

Extraction of the effective doping density profile in irradiated strip detectors