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

This brief presents an NMOS-only voltage reference with small process variations for ultra-low-power applications. All MOSFETs work in the subthreshold region and are biased by the leakage current of the NMOS transistor manufactured in Deep-N-Well (DNW). By fitting the variations of threshold voltage (<inline-formula> <tex-math notation="LaTeX">$\text{V}_{\mathrm{ TH}}$ </tex-math></inline-formula>) from slow/fast corners to typical corners linearly, an optimum body selection (OBS) is proposed to reduce the impact of the process variations from <inline-formula> <tex-math notation="LaTeX">$\text{V}_{\mathrm{ TH}}$ </tex-math></inline-formula> or <inline-formula> <tex-math notation="LaTeX">$\Delta \text{V}_{\mathrm{ TH}}$ </tex-math></inline-formula> with the aid of the body effect. The proposed design was fabricated in a 0.18-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> CMOS process, together with a baseline design without using the OBS. Based on the 25-chip measurement results, the output voltage variation of the proposed design is <inline-formula> <tex-math notation="LaTeX">$0.0035 \sigma /\mu $ </tex-math></inline-formula>, which is 61% smaller than that of the baseline design. Besides, for the proposed design with the OBS, the power consumption is 23pW (27°C), while the die area is 0.003mm2. The temperature coefficient is 52ppm/°C in a temperature range from 0°C to 85°C without trimming. The line sensitivity is 0.03%/V, and the power supply rejection ratio is 47dB at 100Hz.

A 23-pW NMOS-Only Voltage Reference With Optimum Body Selection for Process Compensation

In this work, a four-band (Band 34 and Band 38–40) TD-LTE (Time Division-Long Term Evolution) transmitter (TX) is presented and fabricated in a 0.13µm CMOS technology. The TX adopted a direct up-conversion structure and integrated a fine digital variable gain amplifier (VGA), segmented R-2R ladder DACs, high linearity up-conversion mixers and wide dynamic range programmable gain amplifies (PGA). An optimized automatic bandwidth calibration circuits compensate a targeted 30% process variation. A 1.78% error vector magnitude (EVM) is achieved, with the adjacent channel power leakage (ACPL) ratio below −50dBc at 10MHz bandwidth, 16QAM modulation. The dynamic range of this TX exceeds 90dB with a fine step of 0.5dB, and the third harmonic distortion (HD3) achieves −54dBc. The TX dissipates 150mW at maximum output power.

A four-band TD-LTE transmitter with wide dynamic range and LPF bandwidth calibration

A 0.5-V-supply, 37.8-nW, 17.6-ppm/°C switched-capacitor bandgap reference with second-order curvature compensation

In this brief, compact multi-channel bandpass filters and diplexers are proposed based on dual-coaxial resonators. One coaxial resonator is embedded into the other to form a dual-mode resonator without increasing the size, where the resonant section of one resonator acts as the shielding cavity of the other one. In this way, the two modes of the dual-coaxial resonator are ideally isolated and can be controlled independently. By properly designing the feeding and coupling structures between resonators, the two modes in one dual-coaxial resonator can be excited and coupled to construct different filter channels without influencing each other. Accordingly, multi-channel filters are realized. For verification, a dual-channel and a triple-channel filters are presented. Moreover, the filter channels in a dual-channel filter can be applied to design the diplexer, resulting in a compact size. Experimental results are presented with good in-band responses and high isolation.

Compact Multichannel Filters and Multiplexers Based on Dual-Coaxial Resonators

Direct 12V-to-1 V power delivery has become popular in datacenter applications. Multiple outputs regulated by switching regulators are favorable to reduce the energy overhead. For example, from Fig. 11.2.1, a DDR5 dual in-line memory module (DIMM) requires multiple 1.1 V and 1.8V for core, I/O and word line boost supplies, each has several amperes of peak current. Single-inductor-multi-output (SIMO) design may be a low-cost solution, but it has a low efficiency and cross regulation. A widely used scheme is to supply each output with an independent converter [1]. For the 12V-to-1 V application, the conventional buck converter has a high switching loss. This leads to a low switching frequency $\mathrm{f}_{\text{SW}}$,, and hence a large inductor and low power density. Hybrid converters, such as multi-level converters [2], reduce the voltage stress of switches, and thus can use low-voltage devices with a better figure of merit (FoM). Yet, a large conduction loss takes place due to the stacked low-side (LS) switches, especially when these switches conduct most inductor current in 12V-to-1 V applications. As a result, large switches (area) are necessary to reduce the conduction loss. The dual-inductor hybrid (DIH) converters [3–5] have no stacked LS switches, but using a single inductor is preferable under several-amperes of load current.

11.2 A 12V-to-1V Quad-Output Switched-Capacitor Buck Converter with Shared DC Capacitors Achieving 90.4% Peak Efficiency and 48mA/mm3 Power Density at 85% Efficiency

Mo Huang

Papers

A 23-pW NMOS-Only Voltage Reference With Optimum Body Selection for Process Compensation

A four-band TD-LTE transmitter with wide dynamic range and LPF bandwidth calibration

A 0.5-V-supply, 37.8-nW, 17.6-ppm/°C switched-capacitor bandgap reference with second-order curvature compensation

Compact Multichannel Filters and Multiplexers Based on Dual-Coaxial Resonators

11.2 A 12V-to-1V Quad-Output Switched-Capacitor Buck Converter with Shared DC Capacitors Achieving 90.4% Peak Efficiency and 48mA/mm3 Power Density at 85% Efficiency