Improvement of Electrical Properties of $hbox{Ba}_{{bf 0.7}}hbox{Sr}_{bf 0.3}hbox{TiO}_{bf 3}$ Capacitors With an Inserted Nano-Cr Interlayer

The metal–insulator–metal (MIM) capacitors were prepared with $hbox{Ba}_{0.7}hbox{Sr}_{0.3}hbox{TiO}_{3}hbox{/Cr/Ba}_{0.7}hbox{Sr}_{0.3}hbox{TiO}_{3}$ (BST/Cr/BST) dielectric and Pt electrode. The multilayer BST/Cr/BST was sputtered onto $hbox{Pt/Ti/SiO}_{2}hbox{/Si}$ substrate. The presence of nano-Cr interlayer affects the electrical properties of the capacitors. The temperature coefficient of capacitance (TCC) of capacitors with 2 nm Cr is about 69% of that of capacitors without Cr. In a previous work, the formation of the $hbox{TiO}_{2}$ secondary phase was found after the BST/Cr/BST dielectrics were annealed at 1023 K in $hbox{O}_{2}$ atmosphere for 1 h. It is suggested that the nano-Cr interlayer as a catalyst leads to the $hbox{TiO}_{2}$ formation during the annealing in $hbox{O}_{2}$ atmosphere. The negative value of TCC of BST can be compensated by the positive TCC of $hbox{TiO}_{2}$, and the temperature stability in the dielectric constant can be realized for capacitors with nano-Cr interlayer. The voltage stability of BST is also improved with the insertion of nano-Cr interlayer, and the quadratic coefficient in voltage coefficient of capacitance (VCC) of Pt/BST/Cr(2 nm)/BST/Pt is about 30% of that of the BST capacitor without Cr. The effects of Cr thickness on TCC, VCC, dissipation factor, and leakage current density of Pt/BST/Cr/BST/Pt parallel plate capacitors are investigated.      

Establishment of All Digital Closed-Loop Interferometric Fiber-Optic Gyroscope and Scale Factor Comparison for Open-Loop and All Digital Closed-Loop Configurations

This paper covers the design details of an all digital closed-loop interferometric fiber-optic gyroscope (ADCL-IFOG) prototype, constructed in TUBITAK UME, and scale factor comparison between open-loop and ADCL-IFOG prototypes with sine wave biasing modulation. The output of demodulation circuit, proportional to the applied rotation rate, was sampled by AD7714YN analog-to-digital converter (ADC), operated in 16 bit resolution. Error voltage, generated by microcomputer – controlled LTC 1667CG, 14 bit digital to analog converter (DAC), was sent to the phase modulator through a linear summing circuit to make Sagnac Phase Shift zero, depending on the rotation direction. For this implementation, the ultimate rotation rate of 1.84 ($^{circ}/{hbox{h}}$ ) was nullified. The averaged sensitivity of the proposed closed-loop IFOG in unit of error voltage applied to the phase modulator was determined as 132.65 $mu hbox{V}/(^{circ}/{hbox{h}}$ ). The scale factors of both the open-loop and ADCL-IFOG prototypes were compared in a range of 1–15270 ( $^{circ}/hbox{h}$) rotation rate, corresponding to Sagnac Phase Shifts varying from 0.00115 ( $^{circ}$) to 17.57448 ( $^{circ}$). The maximum peak to peak noise and the bias stability of ADCL-IFOG prototype were determined as 4.97 ($^{circ}/hbox{h}$ ) and 1.48 ($^{circ}/hbox{h}$ ) at 23.0$~^{circ}hbox{C}$ , respectively.      

A 1.2-V CMOS $RC$ Oscillator for Capacitive and Resistive Sensor Applications

An accurate self-adjusting CMOS $RC$ oscillator for capacitive and resistive sensor applications has been designed and manufactured. The oscillator operates with supply voltages from 1.2 to 3 V and achieves an internal accuracy of $pm$ 0.7% with a temperature range from $-20 ^{circ}hbox{C}$ to 60 $^{circ}hbox{C}$. The $RC$ oscillator was fabricated in a 0.35- $muhbox{m}$ standard n-well CMOS process with threshold voltages of 0.5 and $-$0.65 V. Its design and operation are described, and results of measurements performed on the fabricated chips are presented.      

A Study of the Electrochemical Behavior of Poly [N-Vinyl Carbazole] Formed on Carbon-Fiber Microelectrodes and Its Response to Dopamine

N-vinyl carbazole (NVCz) random polymers were electrochemically coated onto micron-size carbon fibers in lithium perchlorate/acetonitrile $({hbox {LiClO}}_{4} /{hbox {ACN}})$, sodium perchlorate/acetonitrile $({hbox {NaClO}}_{4} /{hbox {ACN}})$, and tetraethylammonium tetrafluoroborate/acetonitrile $({hbox {TEABF}}_{4} /{hbox {ACN}})$ solutions in order to form dopamine-sensing layers on the carbon fiber microelectrodes (CFMEs). The resulting micron-thick polymer films were characterized by using scanning electron microscopy and Fourier transform infrared reflectance spectroscopy. Electrocoating of polymeric film was performed by three different electrochemical methods such as cyclic voltammetry and chronoamperometric and chronopotentiometric polarizations. These modified CFMEs were tested against dopamine by applying only cyclovoltammetric techniques. Under optimum experimental conditions, the electrode shows a reversible and stable behavior during 24 days in a 0.1-M ${hbox {TEABF}}_{4} /{hbox {ACN}}$ solution and, hence, can be considered as a promising sensor for dopamine detection. The dopamine detection limit as low as 0.01 nM (3S/N) was obtained for the polymer film formed among applied cyclic voltammetry, chronoamperometry, and chronopotentiometry. The polymer film was demonstrated to offer high selectivity toward dopamine detection in the presence of ascorbic acid.      

Electrical Transport in a Semimetal–Semiconductor Nanocomposite

Measurements are presented on the low-field electrical conductivity and moderate-field current–voltage characteristics in a nanocomposite structure of ErAs particles in an $hbox{In}_{0.53}hbox{Ga}_{0.47}hbox{As}$ host with Be compensation. The electrical conductivity displays strong temperature dependence with two types of transport mechanisms. At ${sim}hbox{205}$ K and above, the low-field conductivity appears to be dominated by free electrons in $hbox{In}_{0.53}hbox{Ga}_{0.47}hbox{As}$. Between 55 and 205 K, the conductivity is well explained by variable-range hopping, $sigma = A exp(-B/T^{1/4}$), via Mott's law. The transport displays a soft breakdown effect at moderate bias fields that grows in threshold field with decreasing temperature. This is attributed to impact ionization of the Be dopants.      

On-Chip Voltage Reference-Based Time-to-Digital Converter for Pulsed Time-of-Flight Laser Radar Measurements

A fully integrated time-to-digital converter (TDC) for a pulsed time-of-flight laser rangefinder has been designed and fabricated by a standard 0.18-$muhbox{m}$ CMOS process. The time-to-digital conversion is realized by counting the full clock cycles of an on-chip ring oscillator between timing signals and by recording the state of its 12 phases at the moment of arrival of the timing signals and their delayed replicas. The frequency of the oscillator is stabilized to an on-chip voltage reference by means of a frequency-to-voltage-converter-based feedback loop. The resolution and single-shot precision (standard deviation) of the TDC are $sim$60 ps and less than $sim$50 ps, respectively, in a range of 80 ns. The worst-case temperature dependence of the TDC is less than 50 $hbox{ppm}/^{circ}hbox{C}$ in the temperature range of 0 $^{circ}hbox{C}$ to 70 $^{circ}hbox{C}$, corresponding to 0.6 $hbox{mm}/^{circ}hbox{C}$ at a distance of 12 m (80 ns). The power consumption of the TDC is less than 18 mW.      

Novel Carbon Dioxide Microsensor Based on Tin Oxide Nanomaterial Doped With Copper Oxide

Carbon dioxide $({rm CO}_{2})$ is one of the major indicators of fire and therefore its measurement is very important for low-false-alarm fire detection and emissions monitoring. However, only a limited number of ${rm CO}_{2}$ sensing materials exist due to the high chemical stability of ${rm CO}_{2}$. In this work, a novel ${rm CO}_{2}$ microsensor based on nanocrystalline tin oxide $({rm SnO}_{2})$ doped with copper oxide (CuO) has been successfully demonstrated. The ${rm CuO}hbox{-}{rm SnO}_{2}$ based ${rm CO}_{2}$ microsensors are fabricated by means of microelectromechanical systems technology and sol-gel nanomaterial-synthesis processes. At a doping level of ${rm CuO}:{rm SnO}_{2} =1:8$ (molar ratio), the resistance of the sensor has a linear response to ${rm CO}_{2}$ concentrations for the range of 1% to 4% ${rm CO}_{2}$ in air at 450$^{circ}{rm C}$. This approach has demonstrated the use of ${rm SnO}_{2}$, typically used for the detection of reducing gases, in the detection of an oxidizing gas.      

Development of a High-k Pr $_{2}$O $_{3}$ Sensing Membrane for pH-ISFET Application

In order to develop a pH sensor having a good pH-sensing characteristic, electrolyte-insulator-semiconductor capacitors using a high-k Pr$_{2}$O$_{3}$ thin film as the sensing membrane were fabricated on silicon substrates by reactive radio frequency sputtering. The structural and morphological features of these films with annealing at various temperatures were studied by X-ray diffraction, atomic force microscopy, and X-ray photoelectron spectroscopy. The Pr$_{2}$O $_{3}$ sensing film after annealing at 900$;^{circ}$C is suggested to the increase in the interfacial SiO $_{2}$ and silicate formation, and the high surface roughness. Therefore, a physical vapor deposition Pr$_{2}$O $_{3}$ film is adopted as a new pH-sensing layer. The result produces a pH response of 52.9 mV/pH $({rm pH}=2hbox{--}12)$, a hysteresis voltage of 17.5 mV $({rm pH}=7 to 4 to 7to 10 to 7)$, and a drift rate of 2.15 mV/h (${rm pH}=7$ buffer solution).      

Comparison of a Multichip 10-V Programmable Josephson Voltage Standard System With a Superconductor–Insulator–Superconductor-Based Conventional System

We developed a 10-V dc programmable Josephson voltage standard (PJVS) using a multichip technique. The PJVS was based on $hbox{NbN/TiN}_{x}/hbox{NbN}$ junctions and operated using a 10-K compact cryocooler. We carried out an indirect comparison with a superconductor–insulator–superconductor-based conventional Josephson voltage standard (JVS) by measuring the voltage of a 10-V zener diode reference standard. The combined standard uncertainty of the comparison was $u_{c} = 0.03 muhbox{V}(k = 1)$, and the relative combined standard uncertainty was $3 times 10^{-9}$.      

Thermal Diffusivity and Related Properties of Colossal Magnetoresistive La$_{0.67}$Ca$_{0.33}$MnO $_{3}$ With Various Grain Sizes

Using the open-cell photoacoustic technique, we have measured the room-temperature thermal diffusivities of the colossal magnetoresistive material La$_{0.67}$Ca$_{0.33}$MnO$_{3 }$, sintered between 1100$;^{circ}$ C and 1350$;^{circ}$ C, with average grain sizes 1, 3, 5, and 10 $mu$m. We obtained the thermal diffusivities by analyzing the phase of photoacoustic signals in thermally thick samples using Calderon's method. We found that the insulator-metal transition temperature does not depend on the grain size ($T_{rm IM} sim 272$ K). However, the thermal diffusivity increases with grain size, with values between 0.431 and 0.969 mm $^{2}$s $^{-1}$. Other related electrical and thermal properties, including the electrical conductivity, thermal conductivity, and phonon mean free path, are also dependent on the grain size. The electronic contribution to the thermal conductivity is 2%–3% of the total thermal conductivity for smaller grain sizes (1–5 $mu$m) and increases to about 24% when the grain size is increased to 10 $mu$ m.      

Synthesis and Characterization of Double-layer Quantum-Dots-Tagged Microspheres

Quantum-dots-tagged poly (styrene-acrylamide-acrylic acid) microspheres (QDsAAMs) were synthesized and modified with hydrazine hydrate through hydrazinolysis. Azidocarbonyl groups, which can be rapidly coupled with proteins under mild conditions, were introduced onto the surface of QDsAAM using azido reaction. Bovine serum albumin (BSA) was selected as model protein to be covalently immobilized on the azidocarbonyl QDsAAM. Instruments such as fluorescence microscope, optical microscope, confocal laser scanning microscope, UV–visible spectrometer, Fourier transform infrared spectrometer, size analyzer, and fluorescence spectrophotometer were used to characterize QDsAAM. Results showed that QDsAAM had a regular double-layer spherical shape and an average diameter of 11.2  $mu$m. It also displayed high fluorescence intensity ( ${lambda}_{{rm ex}}/{lambda}_{{rm em}} = hbox{250}$ nm/370 nm), which showed linearity with concentrations ranging from $hbox{3.0} timeshbox{10}^{-3}$ to $hbox{90.0} times hbox{10}^{-3} hbox{g}{cdot}hbox{L}^{-1}$. In addition, external factors such as pH and ionic strength exerted little influence on fluorescent characteristic. BSA immobilization indicated that QDsAAM with azidocarbonyl groups could be covalently coupled with BSA at the rate of $hbox{40} times hbox{10}^{-3}$ g/g (BSA/QDsAAM), while fluorescence linearity correlation was also found. This functional azidocarbonyl QDsAAM with sensitive fluorescence and active azidocarbonyl groups could be used as a promising fluorescent probe for quantitative detection, protein immobilization, and early rapid clinical diagnostics.      

Smooth Contact Capacitive Pressure Sensors in Touch- and Peeling-Mode Operation

Capacitive (C) pressure sensors typically sense quadratic changes in $C$ as a pressure difference $(P)$ deflects a flexible conducting diaphragm near a rigid ground plane. Touch-mode capacitive pressure (C-P) sensors, where the conducting diaphragm touches a dielectric coated ground plane, often show a more linear response, but with less sensitivity, particularly at low-$P$ . Initial contact of the diaphragm often occurs at a critical $P$. Until $P_{rm crit}$ is reached, the sensitivity is typically too low for accurate measurements. In this work, two different types of electrodes with “parabolic” and “donut” cavity-shapes have been designed, fabricated, and tested to achieve high-sensitivity at low-pressures. A flexible conducting diaphragm touches the bottom electrode smoothly, and both cavity shapes permit initial contact at a zero-pressure differential. This type of C-P sensors can have touch-mode and peeling-mode operations. The sensitivities of these sensors in two operation modes were measured, and their resolutions were smaller than 0.1 Pa at a mean pressure of ${10} ^{5}~{rm Pa}$. Both sensors in two modes have the resolution over total-pressure less than ${10} ^{-6}$, which is difficult to achieve at atmospheric pressure.      

Optimization of Spin-Valve Structure NiFe/Cu/NiFe/IrMn for Planar Hall Effect Based Biochips

This paper deals with the planar Hall effect (PHE) of Ta(5)/NiFe$(t_{rm F})$/Cu(1.2)/NiFe$(t_{rm P})$/IrMn(15)/Ta(5) (nm) spin-valve structures. Experimental investigations are performed for 50 $mu$m$times hbox{50} mu$m junctions with various thicknesses of free layer ( $t_{rm F} = 4, 8, 10, 12, 16, 26$ nm) and pinned layer ($t_{rm P} = 1, 2, 6, 8, 9, 12$ nm). The results show that the thicker free layers, the higher PHE signal is observed. In addition, the thicker pinned layers lower PHE signal. The highest PHE sensitivity $S$ of 196 $mu$V/(kA/m) is obtained in the spin-valve configuration with $t_{rm F} = 26$ nm and $t_{bf P} = 1$ nm. The results are discussed in terms of the spin twist as well as to the coherent rotation of the magnetization in the individual ferromagnetic layers. This optimization is rather promising for the spintronic biochip developments.      

Effect of Factors on Coercivity in Sr–La–Co Sintered Ferrite Magnets

We varied the composition and sintering temperature of Sr–La–Co ferrite magnets to analyze the effects of various important factors on coercivity $(H_{rm cJ})$. We examined the effects of crystal grain size and distribution, the mechanism of magnetization reversal, the degree of crystal grain orientation (OD), and the anisotropy field $(H_{rm A})$ on $H_{rm cJ}$. We proposed an equation based on the experimental results that expresses the measured $H_{rm cJ}$ and considers these effects as $H_{rm cJ} = C_{rm t}(0.4/R_{rm h})$ OD $(H_{rm A} - H_{rm d} - H_{rm in})$, where $C_{rm t}, R_{rm h}, H_{rm d}$, and $H_{rm in}$ are the crystal grain size effects on $H_{rm cJ}$ of sintered magnet, rotational hysteresis integral corresponding to the mechanism of magnetization reversal, demagnetizing field of shape anisotropy, and interaction field between crystal grains, respectively. We found that apart from the volume ratio for single-domain crystal grains and $H_{rm A}$, the mechanism of magnetization reversal had significant effects on $H_{rm cJ}$ for Sr–La–Co sintered ferrite magnets.      

Chalcogenide-Nanowire-Based Phase Change Memory

We report fabrication of phase change random access memory (PRAM) using nanowires (NWs) of GeTe and $hbox{In}_{2}hbox{Se}_{3}$. NWs were grown by a vapor–liquid–solid technique and ranged from 40 to 80 nm in diameter and several micrometers long. A dynamic switching ratio (on/off ratio) of 2200 and $hbox{2} times hbox{10}^5$ was realized for GeTe and indium selenide devices, respectively. The programming power for the RESET operation is only tens of microwatts compared to the milliwatt power levels required by the conventional thin-film-based PRAM.      

Comparison of Alternative Techniques for Characterizing Magnetostriction and Inverse Magnetostriction in Magnetic Thin Films

We compare the direct and inverse techniques of measuring magnetostriction in magnetic thin films. We chose a set of four magnetic thin film samples (Co$_{95}$Fe$_5$, Co$_{60}$Fe$_{20}$B$_{20}$, Ni$_{65}$Fe$_{15}$Co$_{20}$, and Ni$_{80}$Fe$_{20}$) for the measurements, representing positive and negative magnetostriction and having saturation magnetostriction of magnitudes ranging from $10^{-7}$ to $10^{-5}$. We made the direct measurements on a high-precision optical cantilever beam system, and we carried out the inverse magnetostriction measurements on a nondestructive inductive $Bhbox{-}H$ looper with three-point bending stage.      

Planar Optical Waveguide Evanescent Wave ${rm CO}_{2}$ Sensor Based on a Clad of Alstonia Scholaris Leaf Extract

An evanescent wave biosensor is designed and developed using a single mode planar optical waveguide based on a spin coated clad of leaf extract of Alstonia Scholaris. The fabricated sensor showed ${rm CO}_{2}$ concentration dependent response. The specialty of this sensor is that it can be used when stored at room temperature (25$~^{circ}{rm C}$) up to a maximum of 25–30 days with 90% retention of original sensitivity. These ${rm CO}_{2}$ sensing biochips showed good operational efficiency for 10 cycles. The planar optical waveguide is versatile, easy to fabricate and can be used for ppm level ${rm CO}_{2}$ measurement with good sensitivity. Cross sensitivity with respect to humidity is studied. The sensor exhibited a short response time of 4–5 s and recovery time of 25 s with good repeatability and reproducibility.      

Measurement of Rapid Temperature Profiles Using Thermoluminescent Microparticles

The thermal history of a material with initially filled trap states may be probed using thermoluminescence. Since luminescent microparticles are composed of robust oxides, they are viable candidates for sensing temperature under conditions where all other types of direct-contact sensors fail. ${rm Mg}_{2}{rm SiO}_{4}:{rm Tb},{rm Co}$ particles with two thermoluminescent peaks have been heated using micromachined heaters over a 232 $~^{circ} hbox{C}$ to 313 $~^{circ} hbox{C}$ range on time scales of less than 200 ms. The effect of maximum temperature during excitation on the intensity ratio of the two luminescent peaks has been compared with first-order kinetics theory and shown to match within an average error of 4.4%.      

Pileup Correction Algorithms for Very-High-Count-Rate Gamma-Ray Spectrometry With NaI(Tl) Detectors

In this paper, we propose algorithms that are suitable for gamma-ray spectrometric systems with NaI(Tl) detector that support pileup correction at extremely high count rates of $4 cdot 10^{6} hbox{pulses/s}$. The following two algorithms are presented: 1) an algorithm based on modified phase-only correlation (MPOC) for the detection of the beginning of pulses and maximum likelihood estimation (MLE) for the estimation of the pulses' amplitudes and 2) an algorithm based on the modified pulse clipping (MPC) method. Simulation results have shown that the systems based on both MPC and MPOC–MLE are capable of reducing pileup effects and improving the resolution of the energy spectrum at very high count rates. MPOC–MLE can support extremely high count rates while keeping good energy resolution. The resolution of $^{60}hbox{Co}$ at $4 cdot 10^{6} hbox{pulses/s}$ is 7.6%, with only 14% of lost pulses from the channels of interest.      

Modeling and Simulation of a Single Tin Dioxide Nanobelt FET for Chemical Sensors

This paper presents the modeling and simulation of a tin dioxide (${rm SnO}_{2}$) field-effect transistor (FET)-based nanobelt gas sensor. The model results are compared to numerical simulations and experimental data obtained from published results describing the fabrication of single crystal nanobelts grown through thermal evaporation techniques. The fabricated sensor shows good response when exposed to oxygen (${rm O} _{2}$) and hydrogen (${rm H} _{2}$) at room temperature. Gas adsorption causes changes in the electrical contacts due to oxygen vacancies in the bulk. As a result, the ${rm I}$ -${rm V}$ characteristics are very different when the device is exposed to (${rm O} _{2}$) versus (${rm H} _{2}$ ). In the presence of ${rm H} _{2}$, the behavior of the contacts is ohmic and saturation is caused by pinch-off of the channel at the drain contact. However, in the presence of ${rm O} _{2}$ , the behavior of the contacts is Schottky, and device saturation occurs at the source end of the device. Our model is based on a depletion mode MOSFET and it accounts for both ohmic and Schottky contacts when the device is exposed to oxygen or hydrogen. It also provides a possible explanation for the gate bias dependence of the saturation current seen in some published characterization data.