Showing papers on "Temperature coefficient published in 2003"

Effects of TiO2 on sinterability and dielectric properties of high-Q forsterite ceramics

Abstract: High- Q plain forsterite ceramics with Q · f =240,000 GHz were developed by the usual solid sintering process using raw materials of highly purified MgO and SiO 2 . The τ f (temperature coefficient of the resonant frequency) was negative in range −60 to −70ppm/°C. To adjust this to zero we added rutile with high τ f (450ppm/°C). The addition of TiO 2 increased dielectric constant ( e r ), did not affect the Q value, but decreased the sintering temperature by about 100 °C for addition of 0.5 to 10 wt.% TiO 2 . These results were attributed to increasing the sinterability at low temperature by the TiO 2 and the almost pore-free and glassy-phase free grain boundary microstructures. It was not possible to develop a compostion which had τ f =0 ppm/°C, as a result of the chemical reaction between MgO–TiO 2 and TiO 2 during sintering.

Temperature Dependence of GaAs1-xBix Band Gap Studied by Photoreflectance Spectroscopy

Abstract: We performed photoreflectance (PR) spectroscopy in order to investigate the fundamental band gap of GaAs1-xBix alloys. The temperature dependence of the band gap energy was evaluated by analyzing of the Franz–Keldysh oscillation in the PR spectra. With increasing Bi content, the band gap energy of GaAs1-xBix alloy is reduced, which shows a large optical bowing. The temperature coefficient of the band gap decreases appreciably in alloys with increasing Bi content. For x=0.026, the temperature coefficient near room temperature is -0.15 meV/K which is 1/3 of the value for GaAs.

Method and system for temperature compensation for memory cells with temperature-dependent behavior

Abstract: The preferred embodiments described herein relate to a method and system for temperature compensation for memory cells with temperature-dependent behavior. In one preferred embodiment, at least one of a first temperature-dependent reference voltage comprising a negative temperature coefficient and a second temperature-dependent reference voltage comprising a positive temperature coefficient is generated. One of a wordline voltage and a bitline voltage is generated from one of the at least one of the first and second temperature-dependent reference voltages. The other of the wordline and bitline voltages is generated, and the wordline and bitline voltages are applied across a memory cell. Other methods and systems are disclosed for sensing a memory cell comprising temperature-dependent behavior, and each of the preferred embodiments can be used alone or in combination with one another.

Characterization of CaTiO3-NdAlO3 dielectric ceramics

Abstract: An X-ray analysis of the (1−x)CaTiO3–xNdAlO3 tie line revealed solid solubility across the entire compositional range. For x 0.90 exhibit the trigonal structure, characteristic of pure NdAlO3. With the increase in x the permittivity, the temperature coefficient of resonant frequency and the dielectric losses decrease. Ceramics based on the 0.7CaTiO3–0.3NdAlO3 solid solution exhibit τf≈0 ppm/K, er=44 and a Q-value that varies between 30000 and 45000 GHz depending on the cooling rate after the sintering. A microstructural analysis revealed the presence of twin related domains, antiphase boundaries and two types of inclusions rich in Al: hexagonal CaAl12O19-based inclusions and the spinel MgAl2O4, which results from the Mg-based impurities.

Surface acoustic wave device

Abstract: A surface acoustic wave device (e.g., filter or convolver) is designed to increase an electromechanical coupling factor K2 and is basically configured by a substrate, a buffer layer, a piezoelectric layer and an electrode layer. Herein, the substrate is made of a bulk material (e.g., SrTiO3), which allows growth of a perovskite compound crystal being expressed by a general chemical formula of SrZO3 (where Z denotes an element such as Zr and Sn whose valence is 4). The buffer layer is formed on the substrate and is made of the perovskite compound crystal (e.g., SrZrO3, SrSnO3), which has good lattice matching with KNbO3. The piezoelectric layer is made of a KNbO3 single crystal and is formed on the buffer layer with a thickness of 500 nm or so. The electrode layer is formed on or below the piezoelectric layer. An interdigital transducer consisting of input and output electrodes is formed by patterning using photolithography technique being effected on the electrode layer, which is made of a metal material (e.g., Al). In addition, it is possible to form a temperature stabilization layer between the piezoelectric layer and electrode layer. The temperature stabilization layer is made of a material (SiO2) having a temperature coefficient reverse to a temperature coefficient of the piezoelectric layer so as to ease distortion being caused to occur due to differences in thermal expansion between the piezoelectric layer and electrode layer. Incidentally, the temperature stabilization layer has a prescribed thickness, which is approximately 1000 nm.

Improvement in electrical characteristics of graded manganese doped barium strontium titanate thin films

Abstract: Highly (100) textured graded manganese (Mn) doped Ba0.5Sr0.5TiO3 [BST (50/50)] thin films were deposited on lanthanum aluminate substrates using sol-gel technique. We have demonstrated that the graded acceptor doping is a promising technique to reduce the temperature coefficient of capacitance (TCC), loss tangent, and leakage current of BST thin films. In the temperature range between 175 and 260 K the reported TCC of Mn graded BST (50/50) films is less than 5.55×10−4/K, which is comparable to the best capacitors known so far. The lower temperature coefficient of the capacitance of the Mn graded films has been argued to be due to the induced compositional heterogeneity resulting into a distribution of the Curie temperature.

The grain size effect on dielectric properties of BaTiO3 based ceramics

Abstract: In response to the demand for small grain size in thin dielectric layers of multilayer chip capacitors (MLCC), ultrafine powders were synthesized by chemical method. Using the high purity BaTiO3 powders of various grain sizes, temperature-stable dielectric materials of the specification ‘X7R’ were prepared. The effects of the grain size of starting BaTiO3 powders, modifier and sintering temperature on the dielectric properties were investigated. The ceramic grain size was almost proportional to the particle size of the starting BT powders. Sintering below 1280 °C, the ceramics with an average grain size less than 500 nm were obtained, showing a high dielectric constant up to 4150 and temperature coefficient of capacitance (TCC) less than ±15%, which meets the requirement of X7R specification.

Non-spherical nanopowder derived nanocomposites

Abstract: Nanocomposites from nanofillers with preferred form of whiskers, rods, plates and fibers are disclosed. The matrix composition described includes polymers, ceramics and metals. The fillers composition disclosed include inorganic, organic and metallic. These nanocomposites are useful in wide range of applications given their unusual properties such as refractive index, transparency to light, reflection characteristics, resistivity, permittivity, permeability, coercivity, B-H product, magnetic hysteresis, breakdown voltage, skin depth, curie temperature, dissipation factor, work function, band gap, electromagnetic shielding effectiveness, radiation hardness, chemical reactivity, thermal conductivity, temperature coefficient of an electrical property, voltage coefficient of an electrical property, thermal shock resistance, biocompatibility, and wear rate.

Grain boundary electric characterization of Zn7Sb2O12 semiconducting ceramic: A negative temperature coefficient thermistor

Abstract: The electrical properties of the grain boundary region of electroceramic sensor temperature based on inverse spinel Zn7Sb2O12 were investigated at high temperature. The zinc antimoniate was synthesized by a chemical route based on the modified Pechini method. The electric properties of Zn7Sb2O12 were investigated by impedance spectroscopy in the frequency range from 5 Hz to 13 MHz and from 250 up to 600 °C. The grain boundary conductivity follows the Arrhenius law, with two linear branches of different slopes. These branches exhibit activation energies with very similar values; the low-temperature (⩽350 °C) and high-temperature (⩾400 °C) regions are equal to 1.15 and 1.16 eV, respectively. Dissimilar behavior is observed on the relaxation time (τ) curve as a function of temperature, where a single slope is identified. The negative temperature coefficient parameters and nature of the polarization phenomenon of the grain boundary are discussed.

High permittivity and low loss dielectric ceramics in the BaO–La2O3–TiO2–Ta2O5 system

Abstract: Dielectric ceramics were synthesized and characterized in the BaO–La 2 O 3 –TiO 2 –Ta 2 O 5 quaternary system for the three typical compositions: Ba 3 La 3 Ti 5 Ta 5 O 30 , Ba 4 La 2 Ti 4 Ta 6 O 30 and Ba 5 LaTi 3 Ta 7 O 30 , which formed the filled tungsten-bronze structures. The present ceramics indicated high dielectric constant e (127.7–148.1) and low dielectric loss tanδ (in the order of 10 −4 –10 −3 at 1 MHz). Meanwhile, the temperature coefficient of dielectric constant τ e varied from −728 to −1347 ppm/°C with increasing Ba and Ta and decreasing La and Ti concentration in the temperature range of 20–85 °C. The present ceramics are promising candidates for high- e and low loss dielectric ceramics, and the suppression of τ e should be the primary issue in the future work.

Electrical properties of Ni–Mn–Co–(Fe) oxide thick-film NTC thermistors prepared by screen printing

Abstract: Ni–Mn–Co–(Fe) oxide thick films were coated on an alumina substrate by a screen-printing technique. The electrical properties of the thick films, as a function of composition and sintering temperature, were investigated. All the thick-film negative temperature coefficient (NTC) thermistors prepared showed a linear relationship between log resistivity and the reciprocal of the absolute temperature, indicative of NTC characteristics. As the amount of Mn3O4 in (Ni2−x Mn x Co1.0)O4 (0.6≤x≤1.8) thermistors increased, the resistivity and the coefficient of temperature sensitivity decreased to a minimum value and then increased again. Also, at a given Ni–Mn oxide content, the resistivity and the coefficient of temperature sensitivity for (Ni1.0Mn1.0Co1−x Fe x )O4 (0.25≤x≤1.0) and (Ni0.75Mn1.25Co1−x Fe x )O4 (0.25≤x≤0.75) thermistors increased with increasing Fe2O3 content. The influence of composition and sintering temperature on the electrical properties of the thermistors is discussed.

Textile heater with continuous temperature sensing and hot spot detection

Abstract: A soft and flexible heater utilizes electrically conductive threads or fibers as heating media The conductive fibers are encapsulated by negative temperature coefficient (NTC) material, forming temperature sensing heating cables One or more heating cables can be formed into heaters of various configurations including tapes, sleeves or sheets providing simultaneous heat radiation and local overheat protection Such heaters may be connected in different combinations, in parallel or in series The heater may contain continuous positive temperature coefficient (PTC) temperature sensors to precisely control the temperature in the heater Such temperature sensors can be made of electrically conductive fibers, metal wires or fiber optical filaments When required by the heater design, the electrically conductive threads/fibers may have a polymer base, which acts as a Thermal-Cut-Off (TCO) at predetermined temperatures Electrically conductive fibers comprised of such polymer base can melt between 110° C and 350° C thereby terminating electrical continuity in the heater

Microwave dielectric properties of (1−x)CaTiO3–xLi1/2Sm1/2TiO3 ceramics

Abstract: The effect of the bond valence on microwave dielectric properties of (1-x)CaTiO 3-x Li 1/2 Sm 1/2 TiO 3 ccramics was investigated in the range of 00 ≤ x ≤ 10 A complete solid solutions was formed with the orthorhombic perovskite structure in the entire composition range As the Li 1/2 Sm 1/2 TiO 3 content increased, the deviation of the observed dielectric polarizabilities calculated by the Clausius-Mosotti equation from the theoretical values, calculated by the additivity rule of dielectric polarizahility, decreased with increasing bond valence of the B-site in ABO 3 perovskite compound The temperature coefficient of the resonant frequency (TCF) of the specimens decreased, depending on the B-site bond valence in the tilted region (t < 1) Typically, the dielectric constant K= 114, Qf = 3700 GHz, and TCF = 115 ppm/C for the x = 07 composition sintered at 1300 C for 3 h

Temperature characteristics of solidly mounted piezoelectric thin film resonators

Abstract: Solidly mounted piezoelectric thin film resonators (SMRs), which are consisting of a piezoelectric film on alternating laminated low- and high-acoustic-impedance quarter-wave layers on a substrate, are now receiving attention as bulk acoustic wave devices suitable for use in a super-high-frequency range. For practical applications, the temperature dependence of frequency is desirable to be very low. This paper reports the theoretical analysis on the temperature characteristics of the SMR using zinc oxide (ZnO) as the piezoelectric material, silicon dioxide (SiO/sub 2/) as the low impedance material, and ZnO as the high impedance material. The calculated results show that the temperature coefficient of frequency (TFC) varies from -60 ppm//spl deg/C to -27 ppm//spl deg/C with increasing the total layer number. This improvement of TCF results from the positive TCF of SiO/sub 2/. It is also shown that the temperature compensation of the SMR can be achieved by increasing the thickness of the first /spl lambda//4 SiO/sub 2/ layer just below the piezoelectric film or by depositing a thin SiO/sub 2/ capping layer on the piezoelectric film, although the effective electromechanical coupling factor K/sup 2/ and the electric Q decrease a little. Similar theoretical analysis has been performed on the SMRs using ZnO or aluminum nitride (AlN) as the piezoelectric material, molybdenum (Mo) or aluminum nitride (AlN) as the high impedance material, and SiO/sub 2/ as the low impedance material.

Temperature dependence of resonant Raman scattering in double-wall carbon nanotubes

Abstract: The temperature-dependent frequency shift of resonant Raman spectra of double-wall carbon nanotubes is investigated in the range of 78–650 K. We show here that different radial breathing mode (RBM) peaks, which are relative to different tube diameters, have a different temperature coefficient of frequency shift, and the larger diameter carbon nanotubes have more RBM frequency downshift with increasing temperature. We attribute the RBM frequency variation to the temperature dependence of the stretching force constant of C–C bond.

Fiber-optic thermometer using Cr-doped YAlO3 sensor head

Abstract: Cr-doped YAlO3 phosphor crystals have been grown and characterized for applications in fiber-optic thermometers based on the temperature dependence of the photoluminescence (PL) lifetime. PL peaking at λ=735 nm is observed from the crystals following an excitation by a light-emitting diode at λ=520 nm. Long PL lifetime (τ=43.14 ms) is observed from Cr-doped YAlO3 at room temperature as compared with those of ruby (τ=4.2 ms) and spinel (τ=8.0 ms). The temperature coefficient (−0.075 ms/K) of Cr-doped YAlO3 is also larger than those of ruby (−0.010 ms/K) or spinel (−0.037 ms/K). YAlO3 is considered to be a sensitive sensor head material for fiber-optics thermometers.

Dielectric properties of the fluorite-like Bi2O3-Nb2O5 solid solution and the tetragonal Bi3NbO7

Abstract: Our analysis of the microwave dielectric properties of the δ-Bi2O3–Nb2O5 solid solution (δ-BNss) showed a continuous increase in permittivity and dielectric losses with an increasing concentration of Nb2O5. The only discontinuity was found for the temperature coefficient of resonant frequency, which is negative throughout the entire homogeneity range but reaches a minimum value for the sample with 20 mol% Nb2O5. At the same composition there is a discontinuity in the grain size of the δ-BNss ceramics. For the sample containing 25 mol% Nb2O5 two structural modifications were observed. A single-phase tetragonal Bi3NbO7, in the literature referred to as a Type-III phase, is formed in a very narrow temperature range from 850° to 880°C. A synthesis performed below or above this temperature range resulted in the formation of the end member of the δ-BNss homogeneity range. Compared with the δ-BNss the Bi3NbO7 ceramics exhibit lower microwave dielectric losses, an increased conductivity, and a positive temperature coefficient of resonant frequency.

Voltage generation circuitry having temperature compensation

Abstract: Techniques for producing and utilizing temperature compensated voltages to accurately read signals (e.g., voltages) representing data stored in memory cells of a memory system are disclosed. The memory system is, for example, a memory card. The magnitude of the temperature compensation can be varied or controlled in accordance with a temperature coefficient. These techniques are particularly well suited for used with memory cells that provide multiple levels of storage.

Temperature-dependent characteristics of polysilicon and diffused resistors

Abstract: The temperature-dependent characteristics of polysilicon and diffused resistors have been studied. By using 0.18-/spl mu/m CMOS technology, a cobalt salicide process is employed and silicide is formed at the ends of resistors. Based on a simple and useful model, some important parameters of resistors including bulk sheet resistance (R/sub bulk/) and interface resistance (R/sub interface/) are obtained at different temperature. For diffused resistors, the R/sub bulk/ and R/sub interface/ values increase and decrease with increase of temperature, respectively. Positive values of temperature coefficient of resistance (TCR) are observed. Furthermore, TCR values decrease with decreasing resistor size. For polysilicon resistors, the R/sub interface/ values decrease with increase of temperature. In addition, negative and positive TCR values of R/sub bulk/ are found in n/sup +/ and p/sup +/ polysilicon resistors, respectively. In conclusion, by comparing the studied diffused and polysilicon resistors, negative trends of TCR are observed when the resistor size decreases.

Low temperature sintering and crystallisation behaviour of low loss anorthite-based glass-ceramics

Abstract: Anorthite-based glass-ceramics including TiO2 as nucleating agent were melted and quenched in this study. The effect of particle size on the sintering behaviour of glass powders was investigated in order to obtain low-temperature sintered glass-ceramics. Anorthite glass-ceramic starts to densify at the transition temperature of glass (T g = 770°C) and is fully sintered before the crystallisation occurrence (880°C). Therefore, a dense and low-loss glass-ceramic with predominant crystal phase of anorthite is achieved by using fine glass powders (D 50 = 0.45 μm) fired at 900°C. The as-sintered density approaches 99% theoretical density and the apparent porosity is as low as 0.05 Vol%. The dense and crystallized anorthite-based glass-ceramic exhibits a fairly low dielectric loss of 4 × 10−4 at 1 MHz and a thermal expansion coefficient of 4.5 × 10−6°C−1. Furthermore, the microwave characteristics were measured at 10 GHz with the results of K = 9.8, Q f = 2250, and temperature coefficient of resonant frequency τf = −30 ppm/°C.

1 V CMOS current reference with 50 ppm/°C temperature coefficient

Abstract: A CMOS current reference circuit is presented, which can work properly with a supply voltage higher than 1 V By compensating the temperature performance of the resistor, this circuit gives out a current with a temperature coefficient of 50 ppm//spl deg/C over the temperature range of (0/spl deg/C, 110/spl deg/C) and a 05% variation for a supply voltage of 1 to 23 V

High Mn content NiCuZn ferrite for multiplayer chip inductor application

Abstract: The effect of Mn substitution on the magnetic properties and microstructure of the (Ni0.2Cu0.2Zn0.6)1.03(Fe2O3)0.97+0.97xMnO2 (x=0.1–0.5) ferrite sintered at 890 °C were investigated. Mn content increases the initial permeability, but Mn≥0.4 results in the formation of a second phase. The temperature coefficient of initial permeability is strongly affected by the Mn content. When x≥0.3, the temperature coefficient of initial permeability increases quickly. The ferrite can be used in multi-layer chip inductor.

On the temperature coefficient of 4H-SiC BJT current gain

Abstract: In this paper, the temperature coefficient of 4H-SiC NPN BJT current gain is studied by way of numerical simulations. In general, 4H-SiC NPN BJT would have a positive temperature coefficient (PTC) for the common emitter current gain if the acceptor ionization energy is smaller than 170 meV. Both PTC and negative temperature coefficient (NTC) can occur in 4H-SiC NPN BJT with an aluminum-doped base. High base doping concentration is required to obtain a wide range of current density with a NTC for current gain, especially when the electron lifetime in base is low. For a base doping concentration of 2.5×10 17 cm −3 , the NTC for current gain is obtained for current density up to 300 A/cm 2 , even when the electron lifetime is as low as 48 ns. The experimental results are also reported.

Negative temperature coefficient thermistor based on Bi3Zn2Sb3O14 ceramic: An oxide semiconductor at high temperature

Abstract: Bi1.5ZnSb1.5O7 dielectric ceramic with pyrochlore structure was investigated by impedance spectroscopy from 400 to 750 °C. Pyrochlore was synthesized by the polymeric precursor method, a chemical synthesis route derived from Pechini’s method. The grain or bulk resistance exhibits a sensor temperature characteristic, being a thermistor with a negative temperature coefficient (NTC). Only a single region was identified on the resistance curve investigated. The NTC thermistor characteristic parameter (β) is equal to 7140 °C, in the temperature range investigated. The temperature coefficient of the resistance (α) was derived, being equal to −4.46×10−2 °C−1 at 400 °C. The conduction mechanism and relaxation are discussed.