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This work proposes a sensitive low-temperature sensor based on the refractive index (RI) method. It uses a one-dimensional (1D) photonic crystal (PC) structure. The proposed sensor design consists of a bilayer stack of dielectric and superconductor materials. YaBa₂Cu₃O₇ is the superconductor utilized in this case, and we consider air to be the dielectric material. The RI of air doesn’t change much with the temperature, especially compared to the superconductor material. YaBa₂Cu₃O₇ is a superconductor that is ideal for temperature sensing applications because of its temperature-dependent RI. The sensing temperature range for the proposed sensor is 35–70K. The crucial structural factors have been precisely adjusted to increase sensing performance. Based on our knowledge, this is done to increase the sensor’s efficiency to levels that are higher than anything previously reported in the literature. Results show that the designed structure achieves an impressive RI sensitivity of 821.53nm/RIU and a temperature sensitivity of 3nm/K. This sensor could be very useful for medical applications for the detection of low temperatures.

This paper reports the enhancement in the sensing properties of organic dye methyl orange (MO) by introducing TiO₂ nanoparticles. For this purpose, two surface type Ag/MO/Ag and Ag/MO:TiO₂/Ag multifunctional sensors were fabricated by spin coating a 3.0 wt.% solution of MO and 3.0:0.3 wt.% of MO:TiO₂ composite on pre-patterned silver (Ag) electrodes. The gap between Ag electrodes was 40 μm. The Ag/MO/Ag and Ag/MO:TiO₂/Ag structures were characterized to investigate their response towards humidity and temperature variations. The Ag/MO:TiO₂/Ag sensor exhibited better sensitivity and response time than Ag/MO/Ag sensor. The large surface to volume ratio of TiO₂ nanoparticles is the primary reason for the higher sensitivity of Ag/MO:TiO₂/Ag sensor. The sensors can be used to detect humidity variations from 30% to 95% RH and temperature variation from 30°C to 200°C with good stability. Surface morphologies of the film were investigated by scanning electron microscope (SEM).

This paper constructs and simulates the interface circuit of a temperature sensor based on SMIC 0.18 $\mu$m CMOS. The simulation results show that when the power supply voltage is 1.8 V, the chopper op-amp gain is 89.44 dB, the low-frequency noise is 71.83 nV/Hz,${}^{1/2}$ and the temperature coefficient of the core temperature sensitive circuit is 1.7808 mV/${}^{\circ }$C. The sampling rate of 10-bit SAR ADC was 10 kS/s, effective bit was 9.0119, SNR was 59.3256 dB, SFDR was 68.7091 dB, and THD was −62.5859 dB. The measurement range of temperature sensor interface circuit is −50${}^{\circ }$C$\sim +125^{\circ }$C, the relative temperature measurement error is ±0.47${}^{\circ }$C, the resolution is 0.2${}^{\circ }$C/LSB, and the overall average power consumption is 434.9 $\mu$W.

The mesogenic behavior and electronic properties of hydrogen bond ferroelectric liquid crystal (HBFLC) complex are studied using experimental and theoretical techniques. HBFLC complex is synthesized from mesogenic 4-hexyloxy benzoic acid (6O BA) as the proton donor and nonmesogenic chiral DL-tartaric acid (DLTA) as the proton acceptor through intermolecular hydrogen bonding. Molecular geometry of DLTA+6O BA HBFLC complex is optimized by density functional theory (DFT) calculation. An interesting observation is that polarizing optical microscope (POM) study confirms that the HBFLC complex exhibits thermochromic behavior in chiral nematic (N${}^{\ast })$ along with induced nontitled smectic G^* phases. Another noteworthy observation is the manifestation of tripartite temperature stages. Fourier-transform infrared spectroscopy (FTIR) and natural bond orbital (NBO) analysis elucidate the intermolecular hydrogen bond between mesogenic (6O BA) and nonmesogenic (DLTA) compounds. Further, frontier molecular orbital (FMO) study and electrostatic potential (ESP) analysis explore the reactivity sites, intermolecular charge transfer and electronic behavior of HBFLC complex.

This paper presents an energy-efficient and high linearity temperature sensor based on the architecture of a simple on-chip oscillator. A self-calibrated block is proposed to compensate the non-linearities of the on-chip oscillator due to PVT variations. In this manner, this on-chip oscillator-based temperature sensor has superior performance over the conventional inverter-chain-based types. In order to generalize the application, no highly linear temperature coefficient resistors are being utilized. The entire circuit is simple and easy to be scaled down. According to the verifications in 65 nm CMOS process, with one-point calibration, this temperature sensor can achieve an inaccuracy within ±1°C in the temperature range from -55°C to 125°C, with a power consumption of only 0.6 μA under 1.2 V supply voltages.

A self-clocked smart temperature sensor that can be fully integrated and self-contained is introduced in this paper for the first time. The sensor is based on resistive temperature sensing and time-to-digital conversion (TDC). An on-chip RC-based simple oscillator is proposed as the clock source of the sensor. The period of the proposed oscillator tracks the time output of the sensing circuit so that its variation due to RC spread does not affect the temperature sensor’s final digital output. Monte-Carlo simulations show that the sensor achieves an error within $-$1.9/$+$1.21${}^{\circ }$C over a temperature range from 0${}^{\circ }$C to 100${}^{\circ }$C after two-point calibration.

This work suggests an all-digital temperature sensor with a high sampling rate that is based on a time-to-digital converter (TDC). Two on-chip voltage-controlled oscillators (VCOs) are used in the design of the sensor core, which senses temperatures between $-40^{\circ }$C and 200${}^{\circ }$C. For digital code conversion, the outputs of the VCO are fed into two asynchronous counters. In both low- and high- resolution modes, the error following two-point calibration is observed between $-1.08^{\circ }$C and $+1.06^{\circ }$C. The sensor’s ability to function in both high- and low-resolution modes based on conversion time is an important feature. At a sampling frequency of 0.19MHz, the maximum resolution achieved is 0.18${}^{\circ }$C. Additionally, the sensor has control logic built in to turn off the sensing as soon as the conversion is complete. At 90-nm process, 1.1V supply voltage and 27${}^{\circ }$C, the proposed sensor occupies $0.044{\mathrm{\text{mm}}}^2$ and consumes $817.5\mu \mathrm{\text{W}}$.

This work presents an all-digital time-mode subthreshold temperature sensor for monitoring SoC self-heating problem. The sensor incorporated a low-power differential inverter interlaced cascaded delay cell followed by a gated ring oscillator with different temperature coefficients of $-$1736.10 and $-$5880.33 ppm/^∘C, respectively. The differential inverter interlaced cascaded delay cell and XOR gate produce a temperature-dependent large delay pulse, whereas the gated ring oscillator produces temperature-dependent output code for each point of temperature within the delay pulse generated by the differential inverter interlaced cascaded delay cell and XOR. The corresponding temperature code is recorded by an asynchronous counter. At 90-nm CMOS process and 0.6/0.3V supply voltage Vdd, the sensor occupies 0.009mm² and consumes only 876nW at 27^∘C. The sensor has a sampling rate of 52.16KS/s and the resolution is noted to be 0.40^∘C for a temperature span of 0–100^∘C. Besides, the proposed design achieves a very small energy/conversion of 17 pJ, which ensures 2.72 pJ$\times$C² and 0.13 nJ%² resolution FoM and inaccuracy FoM, respectively.

The development of PCR chip shortens the reaction time of DNA amplification, reduces the bulk of reaction reagents; therefore, it is widely applied to biomedicine and other related fields. Since PCR reaction is completed through three different precise temperature zones periodically, the sensitivity of temperature measurement and the heating property of the metal membrane must be highly regarded. In this paper, three kinds of membranes, Ni, Pt, and Ni–Cr, were fabricated on silicon substrates; their resistance–temperature characteristics and heating properties are discussed. The results show that Ni and Pt films have good linear resistance–temperature relationship; the heating property of Pt film is superior to that of Ni–Cr film. The PCR chip with Pt film microheater can reach 150°C in a short time with 25 V voltage.

Microfiber loop resonator (MLR) and microfiber knot resonator (MKR) are fabricated using melt-stretching method for applications in temperature and current sensor, respectively. The MLR is embedded into low refractive index polymer for robustness. Although the spacing of the transmission comb spectrum of the MLR is unchanged with temperature, the extinction ratio of the spectrum is observed to decrease linearly with temperature due to induced changes in the material's refractive index. The slope of the extinction ratio reduction against temperature is about 0.043dB/°C. With the assistance of a copper wire that is wrapped by the MKR, resonant wavelength can be tuned by varying the electric current delivered to the wire. The resonant wavelength change is based on the thermally induced optical phase shift in the MKR due to the heat produced by the flow of electric current over a short transit length. It is shown that the wavelength shift is linearly proportional to the square of current in the copper wire with a tuning slope of 46 pm/A².

We prepared a series of Gd₂O₃:Yb,Er,Ca (3/1/$x$mol.%, $x$ represents the nominal concentration of Ca element including 0, 2, 3, 4, 5, 7, 10) upconversion nanoparticles (UCNPs) with regular morphology via a wet-chemical route. We observed a simultaneous enhancement of upconversion luminescence (UCL) emission of Gd₂O₃:Yb,Er after Ca${}^{2+}$ ions were doped. When the doping level of Ca${}^{2+}$ reaches its optimal concentrate at 5mol.%, the red and green emissions increased by 6.3 and 11 times, respectively. The potential application of Gd₂O₃:Yb,Er,Ca material as a noninvasion optical thermometry based on FIR technique was investigated. The sensing of temperature at both high and room temperatures was realized by choosing different parameters. The absolute temperature sensitivity ($S_a^{\prime }$) of Gd₂O₃:Yb,Er nanoparticles at 293K reached 0.0875K${}^{-1}$, whereas Gd₂O₃:Yb,Er, 5mol.%Ca was chosen as sensor of high temperature due to its considerable Sa of 0.0060K${}^{-1}$ at 573K. The resultant UCNPs provided a new way for sensitive thermal detection at various target temperatures.

The study compares thick-film NTC thermistor devices, produced by the screen-printing (and firing) technique and by the Aerosol Deposition Method (ADM) at room temperature. The devices are compared with respect to film quality (optical, mechanical) and to the negative temperature coefficient of resistance (NTCR) parameters ${\rho }_{25}$ and $B$. While the screen-printed films are porous, the Aerosol Deposited (AD) films are characterized by high tightness, mechanical stability, and a production at room temperature. The electrical analysis shows that the AD films reach the ${\rho }_{25}$- and $B$-values of bulk NTCRs from literature after a moderate tempering step below 400${}^{\circ }$C in air. The screen-printed films show $B$-values that are comparable to the values of bulk NTCRs from literature and ${\rho }_{25}$-values that are significantly higher.

An in situ calcination of an aerosol co-deposited (AcD) NiO-Mn₂O₃ film for the production of a single-phase cubic NiMn₂O₄ spinel film was investigated. Characterizations of the AcD film were performed before, during, and after calcination using SEM, XRD and electrical measurements. It could be shown that in situ calcination to mechanically stable films with single-phase cubic spinel structure is possible. Furthermore, changes in the crystal structure and the NTCR parameters $B$ and ${\rho }_{25}$ during calcination could be shown. After in situ calcination, the electrical properties are similar to those of conventional bulk ceramics.

The intensive up-conversion (UC) photoluminescence and temperature sensing behavior of Er³⁺-doped Bi₇Ti₄NbO₂₁(BTN) ferroelectric ceramics prepared by a conventional solid-state reaction technique have been investigated. The X-ray diffraction and field emission scanning electron microscope analyses demonstrated that the Er³⁺-doped BTN ceramics are single phase and uniform flake-like structure. With the Er³⁺ ions doping, the intensive UC emission was observed without obviously changing the properties of ferroelectric. The optimal emission intensity was obtained when Er doping level was 15 mol.%. The temperature sensing behavior was studied by fluorescence intensity ratio (FIR) technique of two green UC emission bands, and the experimental data fitted very well with the function of temperature in a range of 133–573 K. It suggested that the Er³⁺-doped BTN ferroelectric ceramics are very good candidates for applications such as optical thermometry, electro-optical devices and bio-imaging ceramics.

This paper describes the theoretical investigation of enhancement in temperature sensitivity using one-dimensional (1D) symmetric defective photonic crystal (PC) containing Si (Silicon) and Bi₄Ge₃O${}_{12}$ (Bismuth Germanate, BGO) material. The proposed sensor consists of a defect layer (air defect) sandwiched between two 1D-PCs with a symmetrical and asymmetrical structure composed of Si and BGO, respectively. Sensor performance has been evaluated by calculating the transmittance spectra of the proposed structure. In order to obtain the transmittance spectra, a transfer matrix method (TMM) is employed. The principle of temperature sensing is based on the shift in the resonant wavelength (or peak) of the transmission mode with a change in temperature. This is due to the temperature-dependent refractive index of the Si and BGO layers. Analysis of the transmittance spectra shows that temperature sensitivity of 1D-PC structure can be enhanced by using a symmetric defective PC with and without an external defect layer over asymmetric defective PC. It is found that symmetric defective PC with and without defect shows sensitivity equal to 0.173nm/^∘C and 0.140nm/^∘C, whereas asymmetric defective PC shows 0.125nm/^∘C, for the same parameters. Further, the results show that symmetric defective 1D-PC (without the presence of any external defect layer) gives a higher Q-factor than a symmetric and asymmetric defective 1D-PC with an external defect layer. The proposed structure is cost-effective, easy to fabricate and compact in size.

Semiconductor gas sensors have the inherent problem of drift, which would emerge obviously with the changing of the circumstance temperature. Temperature sensor, and humidity sensor could be added to the gas sensor array to monitor working circumstance of the gas sensors. A series of temperatures was set by a thermostat employed in the experiment system, 20 gas samples (ten for each concentration) were prepared and the response of sensors to these gas samples was sampled. Two different artificial neural networks were used to recognize samples. The response of temperature sensor was introduced into the original networks and eliminated the misjudgments. Drift was suppressed to some extent and the performance of networks was also improved, which eventually verified the validity of the method for temperature drift rejection.