A 65-nm CMOS Self-Supplied Power Management System for Near-Field Wirelessly Powered Biomedical Devices

This paper proposes a self-supplied power management system to efficiently rectify and regulate the AC voltage received from wireless power transmission techniques to power or recharge biomedical devices. The proposed power management system comprises three integrated functional units, namely, a fully cross-coupled rectifier, a self-biased reference voltage, and a capacitor-less low-dropout regulator (LDO). To reduce the current complexity of designing capacitor-less LDOs, a new architecture based on a pair of diode-connected transistors at the load of the LDO is devised which alleviates the need for a large load capacitor. The proposed power management system is implemented in a 65-nm CMOS process with an active chip area of 0.0810 mm2. Experimental results indicate that this system is capable of rectifying an AC signal up to 5 V at a frequency of 6.78 MHz. This rectified signal is then regulated to a fixed DC voltage of 1.75 V, while the load current can vary between 0 and 75 mA, with a maximum voltage dropout of 170 mV. Advantageously, the proposed power management system is significantly robust to temperature, as a 55 °C change in ambient temperature leads to only a 9% degradation in its overall performance. Furthermore, the ability of the power management system to drive low-power consumer electronics is demonstrated, and its superiority is evidenced by a performance comparison with the latest integrated power management systems presented in the literature

Piezoelectric Polymer and Paper Substrates: A Review

Polymers and papers, which exhibit piezoelectricity, find a wide range of applications in the industry. Ever since the discovery of PVDF, piezo polymers and papers have been widely used for sensor and actuator design. The direct piezoelectric effect has been used for sensor design, whereas the inverse piezoelectric effect has been applied for actuator design. Piezo polymers and papers have the advantages of mechanical flexibility, lower fabrication cost and faster processing over commonly used piezoelectric materials, such as PZT, BaTiO3. In addition, many polymer and paper materials are considered biocompatible and can be used in bio applications. In the last 20 years, heterostructural materials, such as polymer composites and hybrid paper, have received a lot of attention since they combine the flexibility of polymer or paper, and excellent pyroelectric and piezoelectric properties of ceramics. This paper gives an overview of piezoelectric polymers and papers based on their operating principle. Main categories of piezoelectric polymers and papers are discussed with a focus on their materials and fabrication techniques. Applications of piezoelectric polymers and papers in different areas are also presented

Advances in Flexible Organic Photodetectors: Materials and Applications

Future electronics will need to be mechanically flexible and stretchable in order to enable the development of lightweight and conformal applications. In contrast, photodetectors, an integral component of electronic devices, remain rigid, which prevents their integration into everyday life applications. In recent years, significant efforts have been made to overcome the limitations of conventional rigid photodetectors, particularly their low mechanical deformability. One of the most promising routes toward facilitating the fabrication of flexible photodetectors is to replace conventional optoelectronic materials with nanomaterials or organic materials that are intrinsically flexible. Compared with other functional materials, organic polymers and molecules have attracted more attention for photodetection applications due to their excellent photodetection performance, cost-effective solution-fabrication capability, flexible design, and adaptable manufacturing processes. This article comprehensively discusses recent advances in flexible organic photodetectors in terms of optoelectronic, mechanical properties, and hybridization with other material classes. Furthermore, flexible organic photodetector applications in health-monitoring sensors, X-ray detection, and imager devices have been surveyed

Multiresonator-Based Printable Chipless RFID for Relative Humidity Sensing

We present a chipless RFID for relative humidity sensing. It consists of three spiral resonators coupled to a 50 Ω microstrip line. One resonator is used for humidity sensing, and the other two are used for encoding ID. The sensing resonator is coated with a humidity sensitive polymer film. As the relative humidity changes the permittivity of the polymer film varies changing the resonant frequency of the sensing resonator. Results show that a dedicated resonator can sense relative humidity over 21–53% range with 2.5 MHz/%RH sensitivity whereas the other two resonators can represent the ID. The sensor does not require any IC and is amenable to low-cost production using printed electronic technology

Ultrasound Sensors for Diaphragm Motion Tracking: An Application in Non-Invasive Respiratory Monitoring

This paper introduces a novel respiratory detection system based on diaphragm wall motion tracking using an embedded ultrasound sensory system. We assess the utility and accuracy of this method in evaluating the function of the diaphragm and its contribution to respiratory workload. The developed system is able to monitor the diaphragm wall activity when the sensor is placed in the zone of apposition (ZOA). This system allows for direct measurements with only one ultrasound PZT5 piezo transducer. The system generates pulsed ultrasound waves at 2.2 MHz and amplifies reflected echoes. An added benefit of this system is that due to its design, the respiratory signal is less subject to motion artefacts. Promising results were obtained from six subjects performing six tests per subject with an average respiration detection sensitivity and specificity of 84% and 93%, respectively. Measurements were compared to a gold standard commercial spirometer. In this study, we also compared our measurements to other conventional methods such as inertial and photoplethysmography (PPG) sensors

Resolving the Unusual Gate Leakage Currents of Thin-Film Transistors with Single-Walled Carbon-Nanotube-Based Active Layers

Solution-processed single-walled carbon nanotube (SWCNT) thin-film transistors (TFTs) in the research stage often have large active areas. This results in unusual gate leakage currents with high magnitudes that vary with applied voltages. In this paper, we report an improved structure for solution-processed SWCNT-based TFTs. The unusual gate leakage current in the improved structure is resolved by patterning the SWCNT active layer to confine it to the channel region. For comparative purposes, this improved structure is compared to a traditional structure whose unpatterned SWCNT active layer expands well beyond the channel region. As TFT performance also varies with oxide layer thickness, 90 nm and 300 nm thick oxides were considered. The improved TFTs have gate leakage currents far lower than the traditional TFT with the same dimensions (aside from the unpatterned active area). Moreover, the unusual variation in gate leakage current with applied voltages is resolved. Patterning the SWCNT layer, increasing the oxide thickness, and reducing the top electrode length all help prevent a rapid dielectric breakdown. To take advantage of solution-based fabrication processes, the active layer and electrodes of our TFTs were fabricated with solution-based depositions. The performance of the TFT can be further improved in the future by increasing SWCNT solution incubation time and reducing channel size

Resolving the Unusual Gate Leakage Currents of Thin-Film Transistors with Single-Walled Carbon-Nanotube-Based Active Layers

Solution-processed single-walled carbon nanotube (SWCNT) thin-film transistors (TFTs) in the research stage often have large active areas. This results in unusual gate leakage currents with high magnitudes that vary with applied voltages. In this paper, we report an improved structure for solution-processed SWCNT-based TFTs. The unusual gate leakage current in the improved structure is resolved by patterning the SWCNT active layer to confine it to the channel region. For comparative purposes, this improved structure is compared to a traditional structure whose unpatterned SWCNT active layer expands well beyond the channel region. As TFT performance also varies with oxide layer thickness, 90 nm and 300 nm thick oxides were considered. The improved TFTs have gate leakage currents far lower than the traditional TFT with the same dimensions (aside from the unpatterned active area). Moreover, the unusual variation in gate leakage current with applied voltages is resolved. Patterning the SWCNT layer, increasing the oxide thickness, and reducing the top electrode length all help prevent a rapid dielectric breakdown. To take advantage of solution-based fabrication processes, the active layer and electrodes of our TFTs were fabricated with solution-based depositions. The performance of the TFT can be further improved in the future by increasing SWCNT solution incubation time and reducing channel size