Zeynep Celik-Butler

Spectral dependence of 1ƒγ noise on gate bias in n-MOSFETS

Abstract The modified McWhorter model that has been developed before to explain the 1 ƒ γ noise in Metal-Oxide-Semiconductor-Field-Effect-Transistors was extended to include frequency dependence of the noise power spectrum on operating voltages. Under the assumption of energy and spatial distribution of traps in the oxide, the drain voltage noise spectrum was calculated for MOSFETs operating in the linear region. Experimentally flicker noise measured on n -channel enchancement-mode MOSFETs up to the frequency of 4 kHz. The actual value of the exponent γ in the 1 ƒ γ spectrum was found to increase with gate bias. Furthermore, it was found that the magnitude of the noise power decreased with gate bias. The detail of the calculations and the experimental results are presented.

A semiconductor YBaCuO microbolometer for room temperature IR imaging

The characteristics of infrared (IR) microbolometer arrays utilizing semiconducting YBaCuO and operating at room temperature are presented. Surface-micromachined structures in the form of 1/spl times/10 arrays of pixel size 40 /spl mu/m/spl times/40 /spl mu/m and 60 /spl mu/m/spl times/60 /spl mu/m as well as single pixels of various geometries were constructed. Using the chopped radiation from a broad-band IR source, the responsivity R/sub V/ of the sensor was measured to be as high as 10/sup 4/ V/W and detectivity D* to be /spl sim/2/spl times/10/sup 7/ cm Hz/sup 1/2//W for a thermal conductance G/spl sim/10/sup -5/ W/K between the detector and the substrate. The spectral response was found to be uniform over a range of 1-12 /spl mu/m. Silicon micromachining and ambient-temperature processing were employed to ensure compatibility and, therefore, potential integration with CMOS-based signal processing circuitry. Methods of enhancing the figures of merit are discussed.

A method for locating the position of oxide traps responsible for random telegraph signals in submicron MOSFETs

Random telegraph signals (RTS) have been measured in the drain to source voltage of W/spl times/L=0.97/spl times/0.15 /spl mu/m/sup 2/ medium-doped drain (MDD) n-MOSFETs. The depth of the trapping center in the oxide is found from the gate voltage dependence of the emission and capture times. The difference in the drain voltage dependence of the capture and emission times between the forward and reverse modes is utilized to find the position of the trap in the channel with respect to the source.

Investigation of semiconducting YBaCuO thin films: A new room temperature bolometer

We explore the application of the semiconducting phases of YBaCuO thin films as a bolometer for uncooled infrared detection. For this study, four different structures were built with different types of buffer layers: YBaCuO on a Si substrate with and without a MgO buffer layer, and on an oxidized Si substrate with and without a MgO buffer layer. These films were all amorphous without a detectable long range order. For comparison, crystalline tetragonal YBa 2 Cu 3 O 6.5 and YBa 2 Cu 3 O 6.3 thin films on a LaAlO 3 substrate were included into the study. All six films exhibited semiconducting resistance versus temperature characteristics. The bolometer figures of merit, responsivity, and detectivity were calculated from the measured temperature coefficient of resistance ~TCR! and the inherent noise characteristics of the temperature sensing element. The room temperature TCRs for all four amorphous films were greater than 2.5% K 21 . The highest TCR of 4.02% K 21 was observed on the amorphous YBaCuO thin film deposited on MgO/Si without a SiO2 layer. The TCR of the tetragonal films, on the other hand, remained 2% K 21 or less in the same temperature range. Noise measurements performed in the 1‐100 Hz frequency range revealed a quadratic dependence on the bias current as would be expected from ohmic electrical characteristics. The Johnson and 1/f regions were clearly identified in the noise spectrum. From TCR and noise measurements, we estimated the amorphous semiconducting YBaCuO bolometers would have a responsivity as high as 3.8310 5 V/W and a detectivity as high as 1.6310 9 cm Hz 1/2 /W for 1 mA bias current and frame frequency of 30 Hz if integrated with a typical air-gap thermal isolation structure.

Determination of Si-SiO/sub 2/ interface trap density by 1/f noise measurements

The concentration of silicon-silicon dioxide interface traps with energies down to within 20 meV of the majority-carrier band edge was determined using 1/f noise measurements. p-type diffused resistors of four-probe geometry were fabricated in a metal-oxide-silicon structure. Flicker noise measurements were performed on these devices at cryogenic temperatures of 20 to 280 K. Using A. L. McWhorters (1957) 1/f noise model and the calculated position of the Fermi level with respect to the valence band edge at each temperature, the density of interface traps was calculated at energy levels corresponding to the position of the Fermi level at that temperature. This technique is proposed as an alternate method to measure the oxide trap and slow interface-state densities with energies close to the band edges. >

Self-supporting uncooled infrared microbolometers with low-thermal mass

A new micromachined microbolometer array structure is presented that utilizes a self-supporting semiconducting yttrium barium copper oxide (Y-Ba-Cu-O) thin film thermometer. The Y-Ba-Cu-O thermometer is held above the substrate only by the electrode arms without the need of any underlying supporting membrane. This represents a significant improvement in the state-of-the-art for microbolometers by eliminating the thermal mass associated with the supporting membrane. The reduced thermal mass permits lowering the thermal conductance to the substrate to obtain increased responsivity or having a shorter thermal time constant to allow for higher frame rate camera. The simple structure does not suffer from warping problems associated with stress imbalances in multilayer microbolometer structures that utilize a supporting membrane such as Si/sub 3/N/sub 4/. Devices were fabricated by growing Y-Ba-Cu-O films on a conventional polyimide sacrificial layer mesa. Subsequent etching of the sacrificial layer provides the air gap that thermally isolates the microbolometer. Y-Ba-Cu-O possesses a relatively high temperature coefficient of resistance of 3.1%/K at room temperature. The 400-nm-thick Y-Ba-Cu-O film exhibited absorptivity of about 30%. The responsivity and detectivity approached 10/sup 4/ V/W and 10/sup 8/ cm Hz/sup 1/2//W to filtered blackbody infrared (IR) radiation covering the 2.5 to 13.5 /spl mu/m band. This extrapolates to noise equivalent temperature difference (NETD) less than 100 mK. The micromachining techniques employed are post-complementary metal-oxide-semiconductor (CMOS) compatible, allowing for the fabrication of focal plane arrays for IR cameras.

Micromachined YBaCuO capacitor structures as uncooled pyroelectric infrared detectors

Uncooled pyroelectric infrared detectors based on semiconducting Y–Ba–Cu–O have been investigated. Samples with four different structures were characterized. Two of the pyroelectric detectors were thermally isolated from the substrate by micromachining techniques for high optical sensitivity. Pyroelectricity was observed by the methods of optical illumination and direct substrate heating. A wide range of the values of pyroelectric coefficients was obtained with the maximum close to 20 μC/cm2 K in one device. Detectivities up to 108 cm Hz1/2/W were measured. The temperature dependence of these pyroelectric sensors was investigated. It was found that one device showed a fairly constant optical response with respect to temperature over a wide range around 300 K. However, responsivity of another device of a different geometry decreased sharply at ∼304 K. The spectral study of these devices showed that the wavelength-dependent response decreased when the silicon transmission increased. In addition, frontside i...

Extraction of oxide trap properties using temperature dependence of random telegraph signals in submicron metal–oxide–semiconductor field-effect transistors

Random telegraph signals (RTS) in the drain voltage of light-doped drain n-metal–oxide–semiconductor field effect transistors with W×L=0.5×0.35 μm2 were investigated in the 300–230 K temperature range. The mean capture and emission times were studied as a function of gate voltage as well as temperature in the RTS. A method was developed where several trap characteristics can be extracted, including the position, barrier energy for capture, enthalpy, and entropy associated with emission of an electron, as well as screened scattering coefficient for carrier mobility as a function of temperature. This article reports on a single trap as an example. The position of the trap in the oxide (Tox=70 A) was found to be 12 A and, as expected, independent of temperature. The mean capture and emission times exhibited an increase as the temperature is decreased, following a thermally activated process. Utilizing these observations and the temperature dependence of the drain current, the gate voltage dependence of the t...

SEMICONDUCTING YBACUO THIN FILMS FOR UNCOOLED INFRARED BOLOMETERS

We have fabricated and measured the performance of semiconducting YBaCuO thin‐film thermometers on silicon for uncooled bolometric applications. Our YBaCuO thermometers have revealed a change in resistance with respect to temperature (dR/dT) as high as 8.2×103 Ω/K at T=294 K and the temperature coefficient of resistance as high as 3.1% K−1 over a 60 K range around room temperature which implies an excellent bolometric response. At 294 K the thermometers had a noise voltage of 0.75 μV/Hz1/2 at the frequency of 30 Hz and the bias current of 1 μA. Using the data above, we calculated that semiconducting YBaCuO bolometers would have a responsivity of 5.5×104 V/W and a detectivity D* as high as 1.3×108 cm Hz1/2/W for 1 μA bias current if integrated with a typical thermal isolation structure.

Micromachined integrated pressure—thermal sensors on flexible substrates

This paper presents the design, modeling and simulation of micromachined, integrated pressure–thermal sensors on flexible polyimide substrates. Finite element simulations were performed with polycrystalline silicon as the piezoresistor material on a suspended Si3N4 layer. These piezoresistors are connected to each other in a half-bridge Wheatstone configuration using flexible aluminum interconnects. Several different designs of integrated thermal–pressure sensors as well as pressure-only sensors were simulated to compute the sensor figures of merit such as the percentage change in piezoresistance in response to normal pressure, piezoresistor Wheatstone-bridge output voltage for varying skin curvature, bolometric response to broadband infrared radiation, thermal time constant and thermal conductance of the micromachined structures hosting the sensors to the substrate. For a perpendicular uniform pressure application of 50 kPa, a maximum Wheatstone-bridge output of 7.59 mV was computed for 1 V bias, corresponding to a piezoresistance change of 1.52%. When the skin is bent to a curvature of 2.2 mm, a maximum Wheatstone-bridge output voltage of 70 mV was calculated for the case when the sensors are aligned along the axis of bending. Thermal and optical calculations performed on the integrated thermal–pressure sensors showed a thermal time constant as low as 12.8 µs for a 1.9 µm thick silicon nitride membrane layer, with a responsivity of 270 V W−1 to a broad-band infrared radiation. This would be appropriate for applications requiring fast response but not high sensitivity. Integrated sensors on a thinner silicon nitride membrane layer of 0.5 µm, on the other hand, exhibited responsivity as high as 2000 V W−1, with a response time of 626 µs.