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This article presents a 16-MHz RC frequency reference implemented in a standard 180-nm CMOS process. It consists of a frequency-locked loop (FLL) in which the output frequency of a digitally controlled oscillator (DCO) is locked to the frequency-phase characteristic of a Wien bridge RC filter. Since it is made from on-chip resistors and capacitors, the filter's characteristic is temperature dependent. To compensate for this, the control signal of the DCO is derived by digitizing the filter's output phase and combining it with the digital output of a Wheatstone bridge temperature sensor. After a two-point trim, this digital temperature compensation scheme achieves an inaccuracy of ±90 ppm from -45 °C to 85 °C. The frequency reference draws 220 $\mu \text{A}$ from a 1.8-V supply, with a supply sensitivity of 0.12%/V and a 320-ppb Allan Deviation floor for a 10-s stride.

This letter describes an NPN-based temperature sensor that achieves a 1-point trimmed inaccuracy of ±0.15 °C (3σ) from -15 to 85 °C while dissipating only 210 nW. It uses a dual-mode frontend to roughly halve the power consumption of conventional frontends. First, two NPNs are used to generate a well-defined PTAT bias current, then this current is sampled and applied to the same NPNs to generate well-defined PTAT and CTAT voltages. These voltages are then applied to a low-power tracking ΔΣ modulator-based ADC, which employs a digital filter to efficiently generate a multibit representation of temperature. A prototype fabricated in a 180-nm BCD process achieves 15-mK resolution in a 50 ms conversion time, which translates into a state-of-the-art resolution FoM of 2.3 pJK2.

The effect of azelaic acid on microstructure evolution and electrical properties of anodic aluminum foil for electrolytic capacitor is studied quantitatively. The azelaic acid is selected as formation solution in the multi-step anodization process, and boric acid is applied for comparison. The field-emission scanning electron microscopy and X-ray diffractometer technologies are used for observation of microstructure and detection of crystallinity, respectively. The electrical properties are tested by LCR meter and T–V tester. The microstructure observation shows that the ‘corn-flake’ structures are taken place by ‘cotton-ball’ ones gradually along with the preparation process, and such phenomenon is more obvious when azelaic acid is used. The pores area of anodic aluminum foil formed in azelaic acid is larger because of the stronger acidity. The formation with azelaic acid induces smaller thickness of oxide film, promotes the formation of crystalline oxide, therefore, a barrier film with higher crystallinity and larger grain size is obtained. The barrier film formed in azelaic acid shows larger specific capacitance, lower withstand voltage and larger leakage current, which needs the multi-step anodization for performance improvement.

Cylinder head is one of the most important parts of heated components in the engine, while cracking due to low strength and large residual stress at high temperature is the main failure mode of cylinder head. With the growing demand of good performance and high reliability, gray cast iron with trace alloying element and optimized annealing process are probably effective ways in obtaining suitable materials. The effect of niobium addition on the microstructure and properties of cast iron used in cylinder head is studied in this paper. The results show that, the tensile strength, toughness, fatigue properties and thermal fatigue properties of gray cast iron are improved by adding trace niobium elements. The specimen with 0.20% niobium shows better comprehensive mechanical properties than others. The addition of trace niobium elements can not only refine the graphite, eutectic cell, carbide and phosphorus eutectic, but also reduce the pearlite lamellar space, thus strengthening the matrix. The cylinder head is made by cast iron with 0.20% niobium addition, and the annealing process of thermal aging is optimized. The residual stress of cylinder head can be maintained at a low level by adopting annealing process with higher holding temperature, longer holding time, lower cooling rate and lower outlet temperature. The analysis of microstructure, mechanical properties and residual stress for niobium alloyed cast iron is helpful for solving the cracking problem of cylinder head, and providing scientific basis for improving engine reliability. Keywords: Cast iron, Microstructure, Mechanical properties, Residual stress, Niobium alloyed

This letter presents a compact, energy-efficient, and low-power Wheatstone-bridge temperature sensor for biomedical applications. To maximize sensitivity and reduce power dissipation, the sensor employs a high-resistance (600 $\text{k}\Omega $ ) bridge that consists of resistors with positive (silicided-poly) and negative ( $n$ -poly) temperature coefficients. Resistor spread is then mitigated by trimming the $n$ -poly arms with a 12-bit DAC, which consists of a 5-bit series DAC whose LSB is trimmed by a 7-bit PWM generator. The bridge is readout by a second-order delta–sigma modulator, which dynamically balances the bridge by tuning the resistance of the silicided-poly arms via a 1-bit series DAC. As a result, the modulator’s bitstream average is an accurate and near-linear function of temperature, which does not require further correction in the digital domain. Fabricated in a 180-nm CMOS technology, the sensor occupies 0.12 mm2. After a 1-point trim, it achieves +0.2 °C/−0.1 °C ( $3{\sigma }$ ) inaccuracy in a ±10 °C range around body temperature (37.5 °C). It consumes 6.6 ${\mu }\text{W}$ from a 1.6-V supply, and achieves 200- ${\mu }\text{K}$ resolution in a 40-ms conversion time, which corresponds to a state-of-the-art resolution FoM of 11 fJ $\cdot \text{K}^{2}$ . Duty cycling the sensor results in even lower average power: 700 nW at 10 conversions/s.

With the development of engine and environmental protection, thermal cracking has become one of the main failure modes of components and materials working under complex thermal conditions. The fatigue microcrack and evolution prediction model of compacted graphite iron under thermal fatigue with variable amplitude is studied in this paper, which is induced by pulsed laser. According to the different length, microcracks shorter than 0.1 mm and longer than 0.3 mm are defined as “secondary microcrack” and “main microcrack”, respectively. Results show that, the secondary microcrack caused by the superimposed high-cycle thermal loading shows different behavior of initiation and propagation with the main microcrack. The propagation of secondary microcrack usually limits in a eutectic cell, because that the energy provided in the high-cycle stage is not enough to break across the eutectic boundary. However, the main microcrack can propagate across the eutectic boundary because of enough energy provided in the low-cycle stage. With consideration of both plastic strain energy density and elastic strain energy density, a modified Paris-type model is proposed based on fractal theory. The threshold ∆Wth is introduced to evaluate the damage contribution of elastic strain energy density. The proposed model is helpful for lifetime prediction of components and materials working under thermal fatigue with variable amplitude.

With the growing demand of good performance and high reliability of the heated components, the cracking failure caused by the complex thermal loading of variable amplitude has become a crucial problem. The collective evolution of surface microcrack for compacted graphite iron under thermal fatigue with variable amplitude is studied in this paper, which is induced by pulsed laser. The thermal microcrack is analyzed with statistic method and fractal method systematically. The result shows that, the secondary microcrack is the primary crack pattern, and the number of main microcrack is the least. As the test goes on, the fractal dimension increases following the Hill’s function. Furthermore, the effect of maximum temperature Tmax and superimposed number NHCF on the crack evolution is investigated. Tmax in the heating stage mainly affects the number of main microcrack. With the increase of plastic strain amplitude, the fractal dimension increases exponentially, and gradually tends to be the critical fractal dimension D0 of 1.395. The superimposed number NHCF in the high-cycle stage mainly affects the number of secondary microcrack. The fractal dimension increases exponentially with the increase of NHCF, and tends to be the critical fractal dimension D0 of 1.404. The analysis of the collective behavior of surface microcrack is helpful for evaluating the damage degree and predicting the lifetime, which can be applied to other materials working under thermal loading of variable amplitude.