The modified micromachined thermopile consists of linearly arranged thermopairs instead of the usual loops. This device
can act as a series of antennas and senses the millimeter wave radiation [1]. The antenna-like operation was
demonstrated by the strong dependence on the polarization. The working principle is similar to the bolometers in that
respect that the absorbed radiation heats up the semiconductor strips, but the temperature increment is sensed by the
Seebeck effect instead of the resistance increment. Therefore there is no read-out current and the voltage output starts
from zero. In the present work we are going to search absorption spectra of the device. It is shown that the resonance
depends mainly on the dimensions and shape of the chip; the linear thermopiles are rather E-field probes. The fabrication
of the device will be also outlined as well as the experimental results.
The electric conduction and low-frequency noise were investigated in silicon nitride-based ceramics doped with different
carbon allotropes as multi-wall carbon nanotubes, black carbon and graphite powder. The electric conduction was found
unstable in time. This instability does not depend on the atmosphere and on the possible variation of the temperature. The
noise spectra show 1/f character, however the magnitude of the noise differ for the different dopants, and strongly
depends on the pressure of sintering. The comparison of the resistance values and the noise magnitudes suggest that the
carbon dopants form percolation networks. The carbon is distributed most likely at the surface of the ceramic particles
like the Swiss-Cheese model.
The principles of the construction of piezoresistive silicone pressure sensors are outlined. The fabrication of sensors with ion-implantation and common silicone wafer technology is described. The simulation of the devices showed that the membrane thickness has a major influence on the sensitivity, while the misalignment is less important. The low-frequency noise spectra of the piezoresistive elements are Lorenzian; the characteristic time constant is about 23 μs. The bias dependence of the spectra is in some degree less than it was expected from the regular V2 scaling. The plateau of the noise spectrum at working conditions is higher with almost 30 dB than the thermal noise. This excess noise is attributed to a trap level; however the origin of this G-R center is not clear yet. The figures of merits of the sensor were also estimated in numerical examples.
An improved analysis of low frequency noise in ploy-Si TFT's is proposed in this paper. We present a simple parameter extraction method for 1/f noise sources in poly-Si TFT's based on a comprehensive model for noise generation. The sources for the low frequency noise are identified as the oxide traps in high current regime and the bulk traps in the grain boundary deletion region in low current regime. For high current regime, a simple and useful formula is developed from the Unified Model, which can be used for crystalline Si MOSFET's and SiGe MOSFET's also. For low current regime the bulk trap density in the grain boundary can be extracted utilizing the expression for the noise density considering the thermal activation of carriers from the traps which induces the fluctuations in the barrier height and hence the current noise. The extraction method is successfully applied to the experimental data from the literature with reasonable values for the noise parameters. The concept of mobility in poly-Si TFT's is elucidated. The work can also explain the experimental observation on the barrier height dependence of the low frequency drain current noise in poly-Si TFT's.
PbS photoconductors have been fabricated by the chemical deposition method onto glass substrates. The investigated samples prepared from layers deposited 20 years ago. The photoconductivity of free and encapsulated detectors was investigated at room temperature. The performance of PbS detectors was practically not changed after long time storage at laboratory conditions, or easily recovered after vacuum treatment at 75 °C. The low-frequency (10Hz...20 kHz) noise spectra were measured in dark and during infrared exposure. The carrier lifetime was determined by measuring the frequency response of the device. The changes of the resistance during infrared and ultraviolet exposure were measured too. After the UV illumination the magnitude of the noise levels did not changed too much, however the character of the spectra has definitely changed. The spectra became similar to 1/f indicating that the dominance of generation-recombination noise is less pronounced. The persistent conductivity increase, which occurred by the ultraviolet light is interpreted as the hydration of the oxidized surface.
KEYWORDS: Sensors, Signal to noise ratio, Diodes, Interference (communication), Resistance, Semiconductors, Silicon, Signal detection, Magnetic sensors, Microwave radiation
In this survey at first the general figures of merit of solid-state sensors as sensitivity, dynamic range and noise equivalent signal are defined. With this the main phenomenological parameters as tangential sensitivity, noise figure, noise temperature, noise resistance is treated, and the usefulness of the tangential sensitivity is emphasized. The difference between the phenomenological parameters and the physical noise is pointed out with examples. Finally the basic noise aspects of some often used classical sensor elements as resistance; Hall-plate and diode are reviewed.
The current-voltage characteristics and the low-frequency noise spectra of p-type Si - Porous Si - Al light emitting diodes were investigated. over 1 V forward biases a reasonable fit was obtained in the Fowler-Nordheim plot. At lower biases, however, an additional current-component appears, which shows a saturating character. This current component is ascribed to trap-assisted tunneling. Any attempts of accurately fitting the I-V characteristic by other known transport mechanisms failed, as reported earlier. The measured noise spectra show 1/f character. While the biasing current was varied from a about 30 microAmps up to several mAs, the noise level remained constant within the measuring error, i.e. the voltage noise is independent of the bias. This is contradictory to the results obtained on uniform resistors, where the noise power scales with I2, or V2. On this reason the observed noise is attributed to the saturating trap-assisted tunneling.
Interdigitated planar photodetector structures were fabricated on semi-insulating GaAs material using ohmic-ohmic and Schottky-Schottky contacts. The dc and pulse response performance of the devices indicate that the devices with Schottky contacts are more suitable for high-speed photodetection and pulse generation. The differences between the two types of devices are interpreted with the difference in contact type, trapping mechanisms, and contact resistance effects.
The planar doped barrier diode being majority carrier semiconductor device has promising application areas in high-frequency and microwave circuits. The paper reviews the main features of diode structures. The different current conducting processes as the thermionic emission, the diffusion, and the tunneling are treated. The design rules for the barrier height also are given, and our own experimental results reported. Microwave diodes and zero bias detectors have been fabricated in RITP on layer structures grown in TUT.
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