Showing papers on "Biasing published in 2000"

High-field electrical transport in single-wall carbon nanotubes

Abstract: Using low-resistance electrical contacts, we have measured the intrinsic high-field transport properties of metallic single-wall carbon nanotubes. Individual nanotubes appear to be able to carry currents with a density exceeding 10(9) A/cm(2). As the bias voltage is increased, the conductance drops dramatically due to scattering of electrons. We show that the current-voltage characteristics can be explained by considering optical or zone-boundary phonon emission as the dominant scattering mechanism at high field.

Current injection emission from a transparent p–n junction composed of p-SrCu2O2/n-ZnO

Abstract: An ultraviolet light-emitting diode (LED) operating at room temperature was realized using a p–n heterojunction composed of transparent conductive oxides, p-SrCu2O2 and n-ZnO. Multilayered films prepared by a pulsed-laser deposition technique were processed by conventional photolithography with the aid of reactive ion etching to fabricate the LED device. A rather sharp emission band centered at 382 nm was generated when a forward bias voltage exceeding the turn-on voltage of 3 V was applied to the junction. The emission may be attributed to a transition associated with the electron–hole plasma of ZnO.

Reducing MOSFET 1/f noise and power consumption by switched biasing

Abstract: Switched biasing is proposed as a technique for reducing the 1/f noise in MOSFET's. Conventional techniques, such as chopping or correlated double sampling, reduce the effect of 1/f noise in electronic circuits, whereas the switched biasing technique reduces the 1/f noise itself. Whereas noise reduction techniques generally lead to more power consumption, switched biasing can reduce the power consumption. It exploits an intriguing physical effect: cycling a MOS transistor from strong inversion to accumulation reduces its intrinsic 1/f noise. As the 1/f noise is reduced at its physical roots, high frequency circuits, in which 1/f noise is being upconverted, can also benefit. This is demonstrated by applying switched biasing in a 0.8 /spl mu/m CMOS sawtooth oscillator. By periodically switching off the bias currents, during time intervals that they are not contributing to the circuit operation, a reduction of the 1/f noise induced phase noise by more than 8 dB is achieved, while the power consumption is also reduced by 30%.

Functional separation of biasing and sustaining voltages in two-frequency capacitively coupled plasma

Abstract: Separation of the effects of rf sources used for biasing the wafer and for sustaining the plasma is studied by measuring the space profiles of net excitation rate of Ar(3p5) for a two-frequency capacitively coupled plasma as a representation of a typical oxide etcher. Measurements were performed in Ar and in CF4/Ar mixtures. For biasing supply operating at low frequency, 700 kHz, it was shown that the effect of the voltage becomes significantly smaller as the sustaining voltage is changed from high frequency, 13.56 MHz, to very high frequency (VHF), 100 MHz, and it even disappears for pulsed operation in mixtures. This is the result of the low dc self-bias at the VHF electrode that allows the high energy secondary electrons to leave the plasma without excessive contribution to ionization and dissociation.

Magnetoresistive sensor having hard biased current perpendicular to the plane sensor

Abstract: The apparatus of the present invention is embodied in a magnetic field sensor having a magnetoresistive element, a magnetic bias layer for biasing the magnetoresistive element with a magnetic field, and an electrical insulator positioned between the magnetic bias layer and the magnetoresistive element. The insulator prevents the flow of electrical current between the magnetoresistive element and the magnetic bias layer and at least a portion of the insulator allows passage of the magnetic field from the magnetic bias layer to the magnetoresistive element such that the magnetoresistive element is biased. The method of the present invention is embodied in a method for fabricating a magnetic field sensor having the steps of forming a magnetoresistive element, forming a lower insulator with a main section and an end section over at least a portion of the magnetoresistive element, forming a magnetic bias layer over the main section of the lower insulator, and forming an upper insulator over the magnetic bias layer and over the end section of the lower insulator, such that the magnetic bias layer is electrically insulated from the magnetoresistive element.

Electrical transport through carbon nanotube junctions created by mechanical manipulation

Abstract: Using an atomic force microscope we have created nanotube junctions such as buckles and crossings within individual single-wall metallic carbon nanotubes connected to metallic electrodes. The electronic transport properties of these manipulated structures show that they form electronic tunnel junctions. The conductance shows power-law behavior as a function of bias voltage and temperature, which can be well modeled by a Luttinger liquid model for tunneling between two nanotube segments separated by the manipulated junction.

Bias and temperature dependence of the 0.7 conductance anomaly in quantum point contacts

Abstract: The 0.7 (2e^2/h) conductance anomaly is studied in strongly confined, etched GaAs/GaAlAs quantum point contacts, by measuring the differential conductance as a function of source-drain and gate bias as well as a function of temperature. We investigate in detail how, for a given gate voltage, the differential conductance depends on the finite bias voltage and find a so-called self-gating effect, which we correct for. The 0.7 anomaly at zero bias is found to evolve smoothly into a conductance plateau at 0.85 (2e^2/h) at finite bias. Varying the gate voltage the transition between the 1.0 and the 0.85 (2e^2/h) plateaus occurs for definite bias voltages, which defines a gate voltage dependent energy difference $\Delta$. This energy difference is compared with the activation temperature T_a extracted from the experimentally observed activated behavior of the 0.7 anomaly at low bias. We find \Delta = k_B T_a which lends support to the idea that the conductance anomaly is due to transmission through two conduction channels, of which the one with its subband edge \Delta below the chemical potential becomes thermally depopulated as the temperature is increased.

A CMOS bandgap reference without resistors

Abstract: Bandgap references add the forward bias voltage across a pn diode with a voltage that is proportional to absolute temperature (PTAT) to produce an output that is insensitive to changes in temperature. The relative weighting of the voltages added is usually adjusted by trimming the ratio of two resistors. Although inexpensive resistors of suitable values are available in analog CMOS processes, the area of such resistors is increased in standard digital processes because silicide is often used to reduce the sheet resistance of the polysilicon and diffusion layers. As a result, the length and area of the required resistors is increased, increasing not only the cost, but also the susceptibility of the reference operation to substrate noise coupling. One way to overcome this problem is to use an extra mask to selectively block the silicide, but this mask also increases the cost. This paper presents a circuit solution to the above problem: a bandgap reference without resistors. It uses only MOS transistors biased in saturation or cutoff. The devices biased in saturation operate in strong inversion, for which accurate device models are usually available, simplifying the design process, especially in digital CMOS technologies.

Method and apparatus for compensating a radiation sensor for ambient temperature variations

Abstract: Methods and apparatus for compensating a radiation sensor for ambient temperature variations. Ambient temperature variations may produce undesirable artifacts in electronic signals output by a radiation sensor. In some cases, such artifacts may detrimentally reduce the dynamic range of the sensor and/or processing circuitry associated with the sensor with respect to radiation of interest. The radiation sensor may be compensated for such undesirable artifacts by, for example, adding an appropriate offset to a sensor bias voltage or a sensor bias current, and/or controlling a temperature of the radiation sensor, based on variations in the ambient temperature.

A 1-V, 8-bit successive approximation ADC in standard CMOS process

Abstract: A 1-V 8-bit 50-kS/s successive approximation analog-to-digital converter (ADC) implemented in a conventional 1.2-/spl mu/m CMOS process is presented. Low voltage, large signal swing sample-and-hold, and digital-to-analog conversion are realized based on inverting op-amp configurations with biasing currents added to the op-amp negative input terminal so that the op-amp input common-mode voltages can be biased near ground to minimize the supply voltage. At the same time, the input and output quiescent voltages can be set at half of the supply rails. A low-voltage latched comparator is realized based on the current-mode approach. The entire ADC including all the digital circuits consumes less than 0.34 mW. An effective number of bits of 7.9 was obtained for a 1-kHz 850-mV peak-to-peak input signal.

High-resolution CdTe detector and applications to imaging devices

Abstract: Using a high quality cadmium telluride (CdTe) wafer, we formed a Schottky junction and operated the detector as a diode (CdTe diode). The low leakage current of the CdTe diode allows us to apply a much higher bias voltage than was possible with the previous CdTe detectors. For a relatively thin detector of /spl sim/0.5 mm thick, the high bias voltage results in a high electric field in the device. Both the improved charge collection efficiency and the low-leakage current lead to an energy resolution of 1.1 keV FWHM at 60 keV for a 2/spl times/2 mm/sup 2/ device and 2 keV for a 10/spl times/10 mm/sup 2/ device at 5/spl deg/C without any charge-loss correction electronics. For astrophysical applications, we have developed a an initial prototype CdTe pixel detector based on the CdTe diode. The detector has 400 pixels with a pixel size of 625/spl times/625 /spl mu/m/sup 2/. Each pixel is gold-stud bonded to a fanout board and routed to a front end ASIC to measure pulse height information for each /spl gamma/-ray photon.

Illuminating electronic device and illumination method

Abstract: The present invention relates to the display and keyboard illumination of battery-operated portable electronic devices using LEDs. In a circuit according to the invention, where a flyback converter is modified into a dedicated converter suitable for using two LEDs, the diode-like operation of the LEDs is utilised. On the other hand, also the small supply power non-pulsation demand of the load, due to the illumination purpose. A specified amount of energy determined by the battery voltage (V batt ) is stored in the coil (L) of a primary circuit until, controlled by a comparator (K), the coil is disconnected from the battery by a switch (SW) and the LEDs allow a current to pass, said current being produced by a voltage exceeding the forward bias voltage caused by the self-induction of the coil, and the LEDs begin to illuminate. Using a control circuit (SWC), comparator t (SWC) causes the switch (SW) to become non-conductive after the coil current reaches a specified threshold level. For example, a small resistor connected between the coil and ground is used for measuring the coil current. (SWC) causes the switch to become conductive again on obtaining at its other input the rising edge of a switching frequency signal. Thus, the supply energy of the LEDs is substantially independent of variations in battery voltage within the normal voltage range of the battery. To reduce the interference caused by the circuit, suppressor circuits can be connected to the circuit in parallel with the switch (SW) and the LEDs.

Principles of substrate crosstalk generation in CMOS circuits

Abstract: Substrate noise injection is evaluated for a 0.25-/spl mu/m CMOS technology, to determine the mechanisms that contribute to substrate crosstalk. At the transistor level, we find that impact ionization current and capacitive coupling from the junctions are the most significant contributors to substrate current injection. An investigation of substrate fluctuations at a circuit level included switching transients, capacitive damping, and separate substrate biasing. This investigation revealed that voltage transients on power-supply lines can be the dominant source of substrate fluctuations. Finally, a statistical analysis of signal cancellation in an integrated circuit was performed. The results indicate that more cancellation will take place for the high-frequency noise components than for the average and low-frequency components. As a consequence, the dc and low-frequency components of the transient that result from an individual switching event can not be neglected even if they are a relatively small fraction of the single transient.

Low-voltage bandgap reference circuit

Abstract: In a bandgap voltage reference circuit in accordance with the present invention, the different-sized emitters of the two bipolar devices of a ΔV BE stage return to ground (or other bias voltage) through separate resistors. The V BE term of the reference device is supplied by a V BE current source through a third resistor. The proportional-to-absolute-temperature (PTAT) term of the reference occurs as the difference of base-emitter voltages ΔV BE between the larger and smaller emitters. An output voltage V out multiplier resistor feeds to the larger emitter through an inverting amplifier. In one embodiment of the invention, the output voltage V out trim at one temperature is obtained by trimming the base-emitter resistor of the “small emitter” device to compensate for the V BE process variation.

A micropower class AB CMOS log-domain filter for DECT applications

Abstract: This paper presents a micropower 2nd-order low-pass filter using the log-domain principle and integrated in a 0.35 µm CMOS process. It has been designed as an anti-aliasing filter for a DECT transceiver with a 45 kHz nominal cut-off frequency. The circuit uses transistors biased in weak inversion without requiring separate wells. It operates at 1.5V supply voltage and its current consumption is 8 µA in idle mode. The log-filter is implemented with an on-chip conditioner which allows for class AB operation. It can process input currents at 5 kHz that are 25 times larger than the 200 nA nominal current. Measurements up to 500 times the bias current have been done, since at 1 kHz the current input is only limited by strong inversion and by the supply voltage.

Structure, hardness, and tribological properties of reactive magnetron sputtered chromium nitride films

Abstract: Chromium nitride (CrN) films with Cr/N atomic ratios of 0.73–1.46 were prepared by reactive dc- magnetron sputtering with Ar as the sputtering gas and N2 as the reactive gas. The application of a negative bias voltage to the substrates and the decrement of the gas flow ratio of N2 to Ar (or FN2/FAr) promoted the growth of CrN films with preferred orientations of (200)+(220), high Cr/N ratios, and high densities. The functional hardness and compressive stress were highly dependent on the magnitude of the bias voltage and the Cr/N ratio that was adjusted by the FN2/FAr ratio during film deposition. The optimal energy conditions for ion impingement on growing CrN films with compact columnar crystal structure, high hardness, and enhanced tribological properties were studied with respect to the modulations of the bias voltages and the Cr/N ratios. The CrN films with high hardness and high wear resistance were synthesized in this study at low bias voltages of −(100–300) V and FN2/FAr ratios of 1–3.

Metal–semiconductor–metal GaN ultraviolet photodetectors on Si(111)

Abstract: GaN metal–semiconductor–metal photoconductive detectors have been fabricated on Si(111) substrates. The GaN epitaxial layers were grown on Si substrates by means of metalorganic chemical-vapor deposition. These detectors exhibited a sharp cutoff at the wavelength of 363 nm and a high responsivity at a wavelength from 360 to 250 nm. A maximum responsivity of 6.9 A/W was achieved at 357 nm with a 5 V bias. The relationship between the responsivity and the bias voltage was measured. The responsivity saturated when the bias voltage reached 5 V. The response time of 4.8 ms was determined by the measurements of photocurrent versus modulation frequency.

Structural and tribological characterization of multilayer ta-C films prepared by filtered cathodic vacuum arc with substrate pulse biasing

Abstract: The filtered cathodic vacuum arc (FCVA) technique is reported to be an effective method for producing high quality hard coatings, but has limitations for preparing thick hard tetrahedral amorphous carbon (ta-C) films by the conventional method of floating conditions. Currently, the multilayer approach is the only way to overcome this limitation, and is of great interest because it enables the fabrication of films with varied thickness and properties to suit the application. A multilayer ta-C film of approximately 1 μm thickness is prepared on a silicon substrate by alternate soft (20 nm thick) and hard (100 nm thick) layers of tetrahedral amorphous carbon. The compressive stress of the film measured using the radius of curvature technique, profiled by stylus, is found to be approximately 5.4 GPa. The bond structure of the film is studied using Raman spectroscopy and is typical of films containing reasonably high sp 3 fractions, with an I D / I G ratio of approximately 0.265. The hardness and elastic modulus of the film are approximately 57 and 550 GPa, respectively, which are fairly high for thick ta-C films. The coefficient of friction and wear rate of the ta-C film against a sapphire counter-face are observed to be relatively low. This investigation finds that the ta-C films of relatively high thickness, with favourable hardness and tribological properties, can be prepared by FCVA with alternate substrate pulse biasing.

Reflection Anisotropy Spectroscopy: A New Probe for the Solid-Liquid Interface

Abstract: Introducing reflection anisotropy spectroscopy (RAS) as a new probe for solid-liquid interfaces, we present results for the Au(110)/electrolyte interface which serves as a model system. We demonstrate that RAS is sensitive to surface phase transitions, step morphology, and electronic surface states. Using an empirical approach, the RA spectra are reproduced and features are identified which reflect the known character of the bias voltage driven (2x1) to (1x1) phase transition. RAS is established as an experimental technique to probe the electronic structure of solid-liquid interfaces in real time to study a wide range of interface properties.

Charge trapping device and method for implementing a transistor having a negative differential resistance mode

Abstract: A charge trapping structure for use with an n-channel metal-insulator-semiconductor field-effect transistor (MISFET) is disclosed. A dielectric layer is formed close to a channel region of the MISFET, and includes a number of trapping sites which are arranged and have a concentration sufficient to temporarily store energetic electrons induced by an electric field to move from the channel into the trapping sites. The trapped electrons set up a counter field that depletes the channel of carriers, and as a bias voltage across the channel increases, the device exhibits negative differential resistance (NDR). The charge trapping structure, as well as the rest of the device, are formed using conventional CMOS processing techniques.

Evidence of band bending observed by electroabsorption studies in polymer light emitting device with ionomer/Al or LiF/Al cathode

Abstract: We report electroabsorption studies of indium–tin–oxide (ITO)/poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] insulating layer/Al light-emitting devices. An ionomer and LiF were used as the insulating layer. The internal electric field was nullified at the same bias voltage of 0.6 V for different cathodes of Al, ionomer/Al, and LiF/Al. The bias voltage is close to the work-function difference between ITO and Al. Average electric field in the emitting layer was reduced by inserting the insulating layers. On the contrary, current density was increased significantly. These observations suggest band bending in the devices with ionomer/Al or LiF/Al cathode.

The frequency behavior of the third-order intercept point in a waveguide photodiode

Abstract: In Hayes's (1993) and Williams's (1996) analyses, the photodiode nonlinearity is attributed to the space charge screening effect. In this paper, the third-order intermodulation distortions of a high frequency, large optical cavity p-i-n waveguide photodiode are characterized up to 18 GHz using a two-tone measurement. At high bias voltage, the third-order intercept point (IP3) of the waveguide photodiode is constant at low frequency and /spl sim/f/sup -3/ at high frequency. This closely agrees with our model, which is based upon variation of the photodiode impedance. The measured IP3 of the same device at low bias voltages indicates the contribution of space charge screening under low bias voltage or severe saturation.

Electric field directed assembly of an InGaAs LED onto silicon circuitry

Abstract: We demonstrate an electrophoretic process for assembling very small devices on a silicon circuit. A 20-/spl mu/m diameter InGaAs LED was fabricated and then released from the substrate by etching a sacrificial layer underneath the diode structure. The diode, placed into a buffer solution over the silicon circuit, was positioned onto the circuit's tin/lead contact electrodes by biasing the contacts to establish an electrophoretic current in the buffer solution. Following removal from the buffer solution, the assembly was heated to reflow the solder. Circuit formation and LED activation is demonstrated by forward biasing the LED using the silicon circuit's contacts.

Highly sensitive infrared temperature sensor using self-heating compensated microbolometers

Abstract: This paper experimentally demonstrates a novel technique that drastically reduces the self-heating effect in microbolometers and which can be used to enhance the response due to infrared (IR). This is accomplished by using two bolometers with tailored thermal parameters, in particular, similar thermal mass but different thermal conductivity. Test devices with responsivity of over 6000 V/W at bias voltage of 3 V have been fabricated. Results indicate that this method is robust even under considerable mismatch of device parameters. We believe that this technique would pave way for realization of relatively simple, low cost and sensitive IR detectors for use in thermometry, imaging and other IR applications.

Driver and method of operating a micro-electromechanical system device

Abstract: A driver for use with a micro-electromechanical system (MEMS) device, method of operation thereof and a MEMS device employing the driver and method. In one embodiment, the driver includes an actuation subsystem that provides an actuation voltage to alter an angle of an optical element of the MEMS device. The driver also includes a bias subsystem, coupled to the actuation subsystem, that applies a bias voltage between the optical element and the actuation subsystem, thereby reducing the actuation voltage.

Linear power amplifier bias circuit

Abstract: A bias circuit suitable for use with a radio frequency linear power amplifier compensates for amplifier gain compression by providing bias current responsive to an amplitude of an RF signal to be amplified at a bias current gain greater than unity. The bias circuit comprises a minimal number of active and passive components and is suitable for implementation in a range of process technologies. Bias current gain may be configured over a range of less than to greater than unity gain by adjusting a reference voltage supplied to the bias circuit and by adjusting a resistor value included within the bias circuit. In implementation, the bias circuit is configured to have a bias current gain that complements a characteristic gain compression associated with a particular radio frequency power amplifier.