Humidity measurement is one of the most significant issues in various areas of applications such as instrumentation, automated systems, agriculture, climatology and GIS. Numerous sorts of humidity sensors fabricated and developed for industrial and laboratory applications are reviewed and presented in this article. The survey frequently concentrates on the RH sensors based upon their organic and inorganic functional materials, e.g., porous ceramics (semiconductors), polymers, ceramic/polymer and electrolytes, as well as conduction mechanism and fabrication technologies. A significant aim of this review is to provide a distinct categorization pursuant to state of the art humidity sensor types, principles of work, sensing substances, transduction mechanisms, and production technologies. Furthermore, performance characteristics of the different humidity sensors such as electrical and statistical data will be detailed and gives an added value to the report. By comparison of overall prospects of the sensors it was revealed that there are still drawbacks as to efficiency of sensing elements and conduction values. The flexibility offered by thick film and thin film processes either in the preparation of materials or in the choice of shape and size of the sensor structure provides advantages over other technologies. These ceramic sensors show faster response than other types.

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Humidity Sensors Principle, Mechanism, and Fabrication Technologies: A Comprehensive Review

There has been a resurgence of complex oxides of late owing to their ferroelectric and ferromagnetic properties. Although these properties had been recognized decades ago, the renewed interest stems from modern deposition techniques that can produce high quality materials and attractive proposed device concepts. In addition to their use on their own, the interest is building on the use of these materials in a stack also. Ferroelectrics are dielectric materials that have spontaneous polarization in certain temperature range and show nonlinear polarization–electric field dependence called a hysteresis loop. The outstanding properties of the ferroelectrics are due to non-centro-symmetric crystal structure resulting from slight distortion of the cubic perovskite structure. The ferroelectric materials are ferroelastic also in that a change in shape results in a change in the electric polarization (thus electric field) developed in the crystal and vice versa. Therefore they can be used to transform acoustic wav...

Processing, Structure, Properties, and Applications of PZT Thin Films

We review and critique the recent developments on multifunctional oxide materials, which are gaining a good deal of interest. Recongnizing that this is a vast area, the focus of this treatment is mainly on high-κ dielectric, ferroelectric, magnetic, and multiferroic materials. Also, we consider ferrimagnetic oxides in the context of the new, rapidly developing field of negative-index metamaterials. This review is motivated by the recent resurgence of interest in complex oxides owing to their coupling of electrical, magnetic, thermal, mechanical, and optical properties, which make them suitable for a wide variety of applications, including heat, motion, electric, and magnetic sensors; tunable and compact microwave passive components; surface acoustic wave devices; nonlinear optics; and nonvolatile memory, and pave the way for designing multifunctional devices and unique applications in spintronics and negative refraction-index media. For most of the materials treated here, structural and physical propertie...

Oxides, Oxides, and More Oxides: High-κ Oxides, Ferroelectrics, Ferromagnetics, and Multiferroics

The digital low dropout regulator (D-LDO) has drawn significant attention recently for its low-voltage operation and process scalability. However, the tradeoff between current efficiency and transient response speed has limited its applications. In this brief, a coarse–fine-tuning technique with burst-mode operation is proposed to the D-LDO. Once the voltage undershoot/overshoot is detected, the coarse tuning quickly finds out the coarse control word in which the load current should be located, with large power MOS strength and high sampling frequency for a fixed time. Then, the fine-tuning, with reduced power MOS strength and sampling frequency, regulates the D-LDO to the desired output voltage and takes over the steady-state operation for high accuracy and current efficiency. The proposed D-LDO is verified in a 65-nm CMOS process with a 0.01-mm2 active area. The measured voltage undershoot and overshoot are 55 and 47 mV, respectively, with load steps of 2 to 100 mA with a 20-ns edge time. The quiescent current is 82 $\mu\textrm{A}$ , with a 0.43-ps figure of merit achieved. Moreover, the reference tracking speed is 1.5 $\textrm{V}/\mu\textrm{s}$ .

A Fully Integrated Digital LDO With Coarse–Fine-Tuning and Burst-Mode Operation

Efficiency in RF energy harvesting systems: A comprehensive review

Owing to its relatively high efficiency, extended transmission range, and less exposure to radio frequency radiation, near-field resonant wireless power transfer (R-WPT) has been widely used in consumer electronics and bio-implants. For most applications, a well-regulated output voltage is required against the coupling and loading variations, and thus a regulation scheme should be employed in an R-WPT system. To achieve an optimal receiver (RX) or overall efficiency, together with a reduced cost overhead, several regulation schemes have been proposed in recent years, where the regulation can be implemented at either the RX or transmitter (TX) side, or both. These regulation schemes have been reviewed and comprehensively discussed in this paper. Hence, the main contribution of this paper is to provide a guideline for designing the regulation scheme in R-WPT systems. Moreover, potential new topologies of regulation are investigated here.

An Overview of Regulation Topologies in Resonant Wireless Power Transfer Systems for Consumer Electronics or Bio-Implants

The two-phase operation of a dc–dc converter has several benefits, when compared with the single phase, including higher efficiency, smaller ripple, faster response, etc. However, it suffers from unbalanced currents between the two phases. This article presents a two-phase three-level buck converter with cross-connected flying capacitors (X-CFLY). The proposed converter suppresses the unbalanced inductor currents in a two-phase operation, through the alternate connection of flying capacitors across the branches. Meanwhile, two-phase and three-level techniques help to achieve a fast transient response and a small output ripple. In addition, we derive the transfer function of the proposed generalized multiphase three-level buck converter with interconnected CFLY for analysis, and design accordingly its power stage and feedback loop. Finally, we validate the proposed converter through the fabrication in a 65 nm CMOS GP process. It achieves a low unbalanced current close to 5 mA and a small output ripple of 50 mV for a load current around 110 mA, and a peak efficiency of about 86%.

A Two-Phase Three-Level Buck Converter With Cross-Connected Flying Capacitors for Inductor Current Balancing

Wireless power transfer (WPT) is currently on the critical point of an explosive growth. Here, as projected in Fig. 22.4.1, we propose a future WPT eco-system of consumer electronics, which includes three layers: 1) wireless charging pads being the fundamental energy plants that can charge a wireless power bank and mobile devices; 2) wireless power banks that get energy from plants and feed mobile devices; and 3) power hungry mobile devices that get energy from all the other sources. To enable the mobile devices charging others without additional hardware, we propose a reconfigurable bidirectional 6.78MHz WPT transceiver (TRX) that reuses the LC resonant tank and 4 area-consuming power transistors for the differential Class-D power amplifier (PA) and the full-wave rectifier. With such WPT TRX embedded, one can provide a first-aid to his/her smart watch or friend's device of which the battery is dying.

22.4 A reconfigurable bidirectional wireless power transceiver with maximum-current charging mode and 58.6% battery-to-battery efficiency

Strontium titanate–niobate (SrNb x Ti 1− x O 3 ) film deposited on a SiO 2 /Si substrate by the argon ion-beam sputtering technique is used to fabricate thin-film resistors and metal–insulator–semiconductor (MIS) capacitors by standard integrated-circuit technology. Results show that the film resistor has superior thermal-sensitivity characteristics within the temperature range of 27–200°C, and the MIS capacitor is highly sensitive to relative humidity. Besides investigating the effects of frequency on the impedance of the film resistor at various temperatures and on the current of the MIS capacitor at low and high relative humidities, the response times of the MIS capacitor to adsorption and desorption of water vapor are found to be reasonably short (15 s and 10 s) and its humidity hysteresis can be greatly suppressed at higher operating voltages.

A new thin-film humidity and thermal micro-sensor with Al/SrNbxTi1−xO3/SiO2/Si structure

This article presents a monolithic hybrid boost converter suitable for a high conversion ratio (CR). It uses two inductors, two cross-connected flying capacitors ( $C_{F}\text{s}$ ), and six power switches, allowing a two-phase operation and $C_{F}\text{s}$ near-soft charging. With the internal voltages halved by the $C_{F}\text{s}$ , the inductor current ripple and voltage stress of the switches decrease, thus allowing a reduction in both power loss and silicon area. In addition, the cross-connected $C_{F}\text{s}$ double the pulsewidth of the control signals, thereby allowing a higher switching frequency even under a very high CR. Moreover, this design shares the large bootstrap capacitors of the high-side NMOS switches and also eliminates the need for an additional bootstrap voltage generation for the stacked NMOS switches, enabling an area-efficient full integration of the bootstrap capacitors. The converter, fabricated in 0.35- $\mu \text{m}$ CMOS, occupies a core area of 0.86 mm2. It achieves a 93.5% peak efficiency when the CR is 4.5, with two 3.3- $\mu \text{H}$ inductors (3010 package), two 0.47- $\mu \text{F}~C_{F}\text{s}$ , and a 2-MHz switching frequency.

Mo Huang

Papers

An Overview of Regulation Topologies in Resonant Wireless Power Transfer Systems for Consumer Electronics or Bio-Implants

A Two-Phase Three-Level Buck Converter With Cross-Connected Flying Capacitors for Inductor Current Balancing

22.4 A reconfigurable bidirectional wireless power transceiver with maximum-current charging mode and 58.6% battery-to-battery efficiency

A new thin-film humidity and thermal micro-sensor with Al/SrNbxTi1−xO3/SiO2/Si structure

A Hybrid Boost Converter With Cross-Connected Flying Capacitors