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We investigated the effect of channel hot carrier (CHC) stressing on the creation of gate oxide defect centers causing random telegraph signals (RTSs) in pMOSFETs. To identify these stress-induced hole traps in the oxide and fully characterize their trapping properties, variable temperature RTS measurements were performed from room temperature down to 215 K and repeated after each stressing interval, up to 1200 s. The trapping properties of the stress-induced defect sites and those present before stress are quantified, including the hole capture and emission activation energies, structural relaxation in the oxide network due to trapping/detrapping, and entropy change as well as the energy level and position of the trap in the oxide. Based on this information, disassociated III-Si and hydrogen bridge defects are identified as the hole trapping centers in SiO2. Difference was observed between the process- and stress-induced traps in the entropy change upon hole emission from the oxide trap to Si channel (electron capture from the Si valence band), implying the possibility of stress-induced structural defects being different than the native ones.

Although it is the worst degradation mechanism, the effect of channel hot carrier (CHC) stressing on random telegraph signals (RTS) has not been given enough attention in pMOSFETs. We report on the effect of CHC stressing on different RTS trap parameters namely screened scattering coefficient which controls the amount of charge carrier mobility fluctuations due to remote Coulomb scattering by the trap, RTS fluctuation amplitude, average capture time and capture cross-section. The generation of positive fixed oxide charge with stressing influences the screened Coulomb scattering of the channel carriers and therefore their mobility, in addition to the commonly accepted self-screening of the channel carriers. The two-dimensional mobility fluctuations model is adopted for analyzing the CHC effect on pMOSFETs. The comparison between theoretically and experimentally obtained screened scattering coefficients points toward the impact of the newly generated positive fixed oxide charge due to stressing. The decrease of the screened scattering coefficient results in increased RTS amplitude and decreased contribution of mobility fluctuations to RTS amplitude. Capture time and capture cross-section also change as the capture cross-section pre-factor has been impacted by the reduction of relaxation energy with stressing.

We report on the investigation of random telegraph signals (RTSs) in pMOSFETs at variable temperatures to identify and characterize the hole traps residing at the oxide–semiconductor interface. Attractive center defects as well as a repulsive center defect are identified with trap location, capture cross section, remote Coulomb scattering coefficient, capture barrier energy, trap binding enthalpy, relaxation energy, and change in entropy with hole emission. The attractive centers responsible for RTS were a pair of dissociated three-coordinated silicon (D-III-Si) defects while the repulsive center was identified as a puckered/back-projected oxygen vacancy defect, [a pair of under-coordinated silicon (III-Si) and over-coordinated oxygen (III-O) defects]. Both contain ${E}\gamma ^{\prime }$ centers. This is the first time when such detailed analysis is reported on the hole traps in SiO2 which are responsible for RTS.

This paper presents a wafer-level vacuum-packaged z-axis capacitive micro accelerometer fabricated on a flexible polyimide substrate and encapsulated by another polyimide superstrate enabling the flexibility, bendability, and portability of both the device and the package. The novel low-cost and low-temperature encapsulation procedure requires a fewer fabrication steps than the processes, where a thin epitaxial Si layer or a full Si wafer with cavity is used as a superstrate. It also provides a better pliability. The fabricated micro accelerometers demonstrated excellent integrity when bowed down to 2-cm radius of curvature with the sensitivity varying between 139 and 174 fF/g, depending on the design, under the application of ±4 g of acceleration. The resonant frequencies varied from 800 Hz for the largest device to 1050 Hz for the smallest device. The results reported here represent the best performing, wafer-level-packaged flexible micro accelerometers to date.

Random telegraph signals (RTS) have been used as a technique for gate oxide defect analyses for the last few decades. The time required by a gate oxide defect to capture and emit an inversion layer carrier can be used to extract the defect energy parameters. The RTS behavior measured at different temperatures can provide sufficient information to determine the structure and physical nature of the responsible defects. In addition, an RTS simulation tool is developed that can successfully reconstruct the RTS traces based on the trap parameters related to the defects. Application of electrical stress results in additional RTS in the output signal, which is believed to be the result of Si–Si bond breakage and creation of hole traps, or reactivation of passivated traps. Stressing the MOSFETs has also resulted in random activation and deactivation of oxide traps. This chapter focuses on the theoretical background of RTS in MOSFETs, sample setup for RTS measurements, data analyses, advantages, and limitations of using RTS to characterize defects.

The effect of channel hot carrier stress has been investigated in pMOSFETs with respect to channel hole trapping by the gate oxide traps and the resultant Random Telegraph Signals (RTS) observed at the output. Process- and stress- induced oxide traps have been identified through RTS measurements. These traps are believed to be E′ centers, acting as hole-attractive or repulsive centers, causing RTS through correlated carrier number and mobility fluctuations. Generation of E′ centers as well as activation of the passivated oxide defects as a result of stress are thought to be the reasons behind observing the stress-induced RTS. Two of the observed defects: one process-induced and one stress-induced trap have disappeared and reappeared randomly with stress. We report the reaction of the defects with hydrogen to be responsible for the volatile nature of the traps. Hydrogen is either bound to the Si/SiO2 interface or trapped at the oxide defects. Applying the stress releases these hydrogen species, which then drift towards the gate through the oxide layer and react with the oxide defects to passivate them. Reaction with another hydrogen de-passivates the defect releasing H2. This is the first article that reports hydrogen to deactivate and reactivate oxide traps responsible for RTS.

A low-temperature deposition process employing aluminum-induced crystallization has been developed for fabrication of piezoresistive polycrystalline silicon (polysilicon) films on low cost and flexible polyimide substrates for force and pressure sensing applications. To test the piezoresistive properties of the polysilicon films, prototype pressure sensors were fabricated on surface-micromachined silicon nitride (Si 3 N 4 ) diaphragms, in a half-Wheatstone bridge configuration. Characterization of the pressure sensor was performed using atomic force microscope in contact mode with a specially modified probe-tip. Low pressure values ranging from 5 kPa to 45 kPa were achieved by this method. The resistance change was found to be − 0.1% to 0.5% and 0.07% to 0.3% for polysilicon films obtained at 500 °C and 400 °C, respectively, for the applied pressure range.

Nanocrystalline piezoresistive polysilicon films were obtained at low temperatures by aluminum-induced crystallization (AIC). The films exhibited granular structure with good polycrystalline properties. A piezoresistive pressure sensor was fabricated on a polyimide substrate, in a Wheatstone bridge configuration comprising two passive resistors and two active piezoresistors made of polysilicon films obtained by AIC. The resistors showed linear I-V characteristics with typical resistance values between 15 and 30 kΩ . Atomic force microscopy was used in contact mode to study the response of the pressure sensor with applied pressure in the 2-19 kPa range. For the higher range of 450 kPa-2 MPa, a load-cell with a nanopositioner was utilized. The pressure-sensor sensitivity was measured to be 41.12 and 5.02 mV/MPa, respectively, for these ranges, when the Wheatstone bridge was bias at 1 V.

Low frequency noise measurements were performed on n- and p-channel MOSFETs with TaSiN and TiN metal gates, respectively, deposited on ALD HfO2 gate dielectric. Lower normalized current noise power spectral density is reported for these devices in comparison to poly-Si/HfO2 devices and that yielded one order lower magnitude for extracted average effective dielectric trap density. In addition, the noise levels in PMOS devices were found to be higher than NMOSFETs and the dielectric trap distribution less dense in the upper mid-gap than the lower mid-gap region. The screened carrier scattering coefficient extracted from the noise measurements was approximately the same for metal and poly-Si high-k stacks but higher than that for the poly-Si SiO2 system, implying higher Coulomb scattering effects. It is believed that the elimination of dopant penetration seen in poly-Si system and low thermal budgets for metal gate deposition helped lower the noise magnitude and yielded better mobility and effective trap density values.

This paper reports on the design, fabrication, and characterization of device-level vacuum-packaged microbolometers on rigid Si wafers and flexible polyimide substrates. Semiconducting yttrium barium copper oxide (commonly, referred to as YBCO) serves as the bolometric material. Operating micromachined bolometers in vacuum reduces the thermal conductance G(th) from the detector to the substrate. If flexibility of the substrate is not to be sacrificed, then the vacuum packaging needs to be done at the device level. Here, the microbolometers are fabricated on a silicon nitride support membrane, isolated from the substrate using surface micromachining. Suitable materials as well as various dimensions in the vacuum cavity are determined using finite-element method (FEM)-based CoventorWARE. A vacuum cavity made of Al2O3 has been designed. The thermal conductance G(th) of bolometers with the geometry implemented in this work is the same for devices on rigid and flexible substrates. The theoretical value of G(th) was calculated to be 4.0 x 10(-6) W/K for devices operating in vacuum and 1.4 x 10(-4) W/K for devices operating at atmospheric pressure. Device-level vacuum-packaged microbolometers on both rigid Si and flexible polyimide substrates have been fabricated and characterized for optical and electrical properties. A low thermal conductance of 1.1 x 10(-6) W/K has been measured six months after fabrication, which implies an intact vacuum cavity.

A novel piezoelectric micro-energy generator is presented, which converts the mechanical vibrations into electricity by utilizing the piezoelectric effect of zinc oxide nanowires (ZnO NW). This is the first time an integrated energy harvester is built where vertically standing NWs are directly coupled to a MEMS proof-mass for maximum conversion of the vibration energy while maintaining the size in the order of hundreds of micrometers. Hydrothermal growth of nanowires combined with MEMS surface micromachining technology and LIGA is employed to fabricate the device. Patterned SU-8 photoresist confines the growth area of the NW block, located between the silicon substrate and a suspended silicon nitride membrane, on which a nickel proof-mass is electroplated. A piezoelectric potential between the two ends of the NW block is formed once compressed by the membrane due to external vibration. A maximum power of 42 pW across 5.5 MΩ load is measured at the vibration frequency of 40 Hz with an acceleration of 1.4g. The corresponding output voltage is 14.7 mV.

Micromachined infrared sensor arrays have been fabricated on flexible polyimide substrates using a silicon wafer carrier during the fabrication process. These flexible polyimide substrates containing the micromachined infrared sensors were removed from the silicon wafer at the end of fabrication. The fabrication technique utilized surface micromachining of a bridge structure to form the thermal infrared (IR) sensors on flexible substrates. Semiconducting yttrium barium copper oxide YBCO was used as the radiation sensitive material. 1 × 10 sensor arrays of microbolometers were micromachined using a photo-definable polyimide sacrificial layer and characterized before and after removal of the substrate from the Si wafer carrier. The flexible infrared microsensors showed similar performance to microbolometers fabricated on rigid silicon substrates. The YBCO thermistors exhibited a temperature coefficient of resistance (TCR) of ∼−3.4% K−1 near room temperature. Responsivity and detectivity values as high as 6.1 × 104 V/W and 1.2 × 108 cm Hz1/2/W, respectively, were measured in vacuum for a 40 μm × 40 μm microbolometer with 1 μA bias. The lowest observed noise equivalent power was 4.1 × 10−11 W/Hz1/2 while the lowest thermal time constant was 5.7 ms.

1/f noise was measured on lateral bipolar PNP transistors over a temperature range of 220

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...

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.

Random telegraph signals (RTS) have been investigated in the drain to source voltage of Weff×Leff=1.37×0.17 μm2 medium-doped drain (MDD) n-type MOSFETs. The emission (τe) and capture (τc) times of the probed trap were studied as a function of gate voltage as well as substrate voltage. The small size and high doping density of the n-MOSFETs studied create a strong electric field in the MOSFET inversion layer, which makes the surface conduction band split into discrete energy levels. Therefore, modified expressions of τe and τc including the influence of bulk bias (VSB), which changes the degree of quantization, are presented. The trap position in the oxide with respect to the Si–SiO2 interface, and the trap energy, were calculated from the gate voltage dependence of the emission and capture times under different bulk bias conditions. The behavior of the emission and capture times predicted by the two-dimensional (2D) surface quantization effects is in qualitative agreement with the experimental results. The RTS amplitude (ΔVDS/VDS) shows a positive dependence on VSB. The coefficient α for screened oxide charge scattering was calculated at different gate voltages and bulk bias from the RTS amplitude. In addition, the theoretical calculation of the scattering coefficient α, using a 2D surface mobility fluctuation model, was presented, which shows a good agreement with the experimental data.

Random telegraph signals (RTS) have been used to characterize oxide traps of W×L=0.97×0.15 μm 2 medium-doped drain n-MOSFETs. RTS have been measured in the linear and saturation regions of operation, both in forward and reverse modes where the drain and source are reversed. The contribution of mobility fluctuations as well as number fluctuations to the amplitude of RTS has been investigated. The scattering coefficient due to screened Coulomb scattering effect is computed from the measured data as a function of channel carrier density. The depth of the position of the trap in the oxide from Si–SiO2 interface is calculated utilizing the dependence of the emission and capture times on the gate voltage. In addition, the position of the trap along the channel with respect to the source is obtained using the difference in the drain voltage dependence of the capture and emission times between the forward and reverse modes. Knowing the location of the trap in the oxide and along the channel, the energy associated with the trap can be extracted accurately from the data. This technique allows one to evaluate the trap energy at the point where the trap is located without any assumptions about the location of the trap or the need for variable temperature measurements. The probed trap was found to be an acceptor type center (repulsive for an n-MOSFET) located at about 27 A deep the oxide, half-way between drain and source with an energy of ECox−ET=3.04 eV, slightly above the conduction band edge.

Medium doped drain n-MOSFET with W eff × L eff = 0.29 × 0.20 μm 2 have been used to investigate complex random telegraph signals (RTS) in the drain to source voltage. Four-level switching events were observed, from which three discrete traps were distinguished. Their behavior was observed in the range of gate-to-source and drain-to-source voltages of 0.5–1.8 V, all in strong inversion. The capture and emission times of each trap were investigated as a function of gate bias as well as drain voltage. Using the mark-space ratio of the switching events, the position of the traps from the Si–SiO 2 interface was calculated to be about 0.43, 0.55 and 0.74 nm. These evaluations were used successfully to determine the trap energy level with respect to oxide conduction band edge. Comparative evaluation of the mobility fluctuations with respect to number fluctuations was done using RTS amplitude. The screened scattering coefficient due to the Coulomb scattering effect was examined with respect to the variation of carrier density in the channel as well as in the drain voltage for all three traps. An influence of one trap on another was observed and found that there is a change of the energy level of 0.06 eV due to this effect.

This paper describes a new micromachining technique for fabrication of semiconducting yttrium barium copper oxide (YBCO) microbolometers using magnesium oxide (MgO) as the sacrificial layer. This type of bolometer can be operated at room temperature, providing a low-cost alternative for more expensive cryogenically cooled thermal detectors used for infrared (IR) imaging. The new micromachining techniques described here would enable the fabrication of YBCO IR focal plane array (FPA) with CMOS signal processing circuitry. Devices were fabricated by growing YBCO films on 4000-/spl Aring/-thick suspended Si/sub 3/N/sub 4/ membranes measuring 40/spl times/40 /spl mu/m/sup 2/ in area and extended over micromachined air gaps, which provide the low thermal conductivity that is required for high responsivity. The gap was created by etching an MgO sacrificial layer. This is the first example of using MgO in this type of application. The MgO sacrificial layer technique is fully CMOS compatible and presents no major fabrication challenges. Thermal conductivities achieved in vacuum with the Si/sub 3/N/sub 4/ suspended structures were on the order of 10/sup -7/ W/K, yielding an effective thermal isolation for bolometer operation. Optical characterization has shown responsivity up to 60 kV/W and detectivity over 10/sup 8/ cm.Hz/sup 1/2//W to black-body IR radiation, indicating that this technology is a suitable candidate for low-cost thermal imaging.

A study on the dielectric and pyroelectric properties of nonmetallic, polycrystalline Y—Ba—Cu—O thin films was performed for a range of temperatures (170–360K) and frequencies (2 Hz—1kHz). The complex permittivity, as a function of frequency, relaxed according to a first-order Debye Model. This relaxation was shown to be thermally activated, with an activation energy equal to the activation energy for the dc conduction of the material. The behavior of the data indicates that the polarization source is localized carriers near the Fermi level. Pyroelectricity was measured over a temperature range of 170–290 K, showing a constant response over these temperatures. Moreover, the pyroelectric properties of YBCO exhibited a strong sensitivity to poling at elevated temperatures, with a dramatic increase in the magnitude of the response. The pyroelectric coefficient changed from p ≈ 400 nC/(cm2-K) for the unpoled case to p ≈ 20 μC/(cm2-K) after poling with 5000 V/cm for one hour at 320 K.

Low-frequency measurements were performed on W-plug via structures connecting two TiN/Al-0.5%Cu/TiN levels in order to evaluate the potential application of noise measurements as a characterization tool for electromigration reliability. Noise measurements were performed with ambient temperature ranging from 87°C to 180°C and applied current from 5.9 to 23.8 mA through 1.0 μm and 0.8 μm vias, corresponding to sample temperatures up to 195.2°C. The noise spectral density was found to be in the form of 1ƒ. The noise magnitude was consistently higher for both vias when the electron flow was from upper level to lower level compared to the opposite direction. The noise activation energy Ea obtained from the temperature dependence of voltage noise power spectral density at 10 Hz showed different behavior for the 1.0 μm via compared to the 0.8 μm via. For the smaller via, Ea = 0.36–0.37 eV regardless of the electron flow direction, whereas for the larger via, Ea = 0.47 eV for electron flow from upper level to lower level and Ea = 0.37 eV for electron flow from lower level to upper level.

Al-Cu-Si TiW multilayered via electromigration behavior was researched using the low frequency noise method. Noise measurements were performed with ambient temperature ranging from 100 to 200°C and applied current density from 5.3 × 10 5 to 3.3 × 10 6 A cm −2 , corresponding to sample temperatures up to 276°C. The noise spectral density was found to be in the form of 1 f γ with 0.95≤ γ ≤1.15, which corresponds to 1 f noise. The noise magnitude was independent of the electron flow direction at relatively low current densities and temperatures. However, for J ≥ 2.6 × 10 6 A cm −2 and T ambient ≥ 180°C ( T sample ≥228°C), the noise for electron flow out of the via was higher than that for electron flow into the via. At low current densities, the noise spectrum showed a quadratic dependence on current for both electron flow directions. However, at high current densities, the current exponent depended on the direction of electron flow. The average activation energy, E a , was found to be 0.11 eV when noise measurements were done on the same via sample for both current directions. When different samples were used for different current directions, a 0.23 eV activation energy value was observed. We interpret the first case as a very low-frequency pseudo-a.c. measurement, and the second case as a true d.c. measurement. In both cases, the activation energy did not depend on the direction of the electron flow. These activation energy values are small compared to the results obtained by the median time-to-failure method. The results are interpreted in terms of the electron mobility fluctuations due to fluctuations in the number of migrating vacancies.

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.

We measured 1/f noise on Hg/sub 0.71/Cd/sub 0.29/Te Metal-Insulator-Semiconductor (MIS) infrared detectors operated over the temperature range of 40 K to 90 K under 300 K Infrared (IR) radiation. The purpose of the study was to identify the sources of 1/f noise, especially in relation to the dark current. The devices were operated in the correlated double sampling mode where the voltage across the MIS capacitor was sampled at empty potential well and right after the accumulation of minority carriers in the well due to IR radiation generation. The noise power spectral density for the charge integrated in the MIS well was investigated in relation to the dominant component of dark current. At lower temperatures T/spl les/65 K, the charge noise power spectral density was found to depend quadratically on the dark current. At higher temperatures, this quadratic dependence did not exist. We attribute the dark current to a mixture of tunneling and depletion-region-originated minority carrier generation which seems to be responsible for 1/f fluctuations in these structures for temperatures below 65 K. >

A nanoelectromechanical (NEMS) piezoelectric energy harvester using crystalline ZnO nanowires is developed. The device converts ambient vibrations into usable electrical energy for low power sensor applications. This is accomplished by mechanical excitation of an ordered ZnO nanorod array using a suspended bulk micromachined proof mass. The device is capable of generating up to 14.2 mV single polarity voltage under an input vibration of amplitude 1 g (9.8 m/s2) at a frequency of 1.10 KHz. To realize this structure, highly ordered arrays of crystalline ZnO nanorods have been fabricated using an amorphous silicon template patterned by thermal nanoimprint lithography, in conjunction with a low temperature hydrothermal growth process.

This paper presents the flicker noise or 1/f-noise measurement of RF sputtered amorphous silicon temperature sensors. The temperature sensor was fabricated between a polyimide substrate and superstrate to place it on a zero stress plane. The effects of flicker noise and voltage dependence of noise voltage power spectral density of the sensor were evaluated. The average value of flicker noise coefficient or normalized Hooge parameter K 1/f was found to be 1.2×10−11.

A model for 1 f noise is developed that is based on fluctuations of the number of energy states associated with extended defects and the defect gradient. The tendency for the source of the states such as dislocations to equilibrate by diffusion leads to a 1 f spectral distribution of the effective number of states. When the states are near the Fermi level and active in processes such as carrier recombination or tunneling in semiconductor devices, the fluctuations appear as 1 f noise in voltage or current. The model is quantitative and predicts low noise for a very uniform density of defects or very small defect size. The Hooge dimensionless constant is identified in terms of the defect structure.

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-MOSFET's. 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.

Low-frequency (LF) noise measurements were performed on aluminum thin films biased at current densities of 5 × 10 5 to 3 × 10 6 A/cm 2 at different temperatures up to 200°C. Correlation between the mechanisms causing these LF fluctuations and electromigration was investigated. Contrary to the 1/ f 2 form observed by other researchers, we observed 1/ f γ noise spectra where γ varied between 0.8 and 1.5. Through the Arrhenius plot of noise power spectral density, activation energies ranging from 0.60 to 0.69 eV have been obtained which agree with activation energies obtained through 1/ f 2 noise measurements. These values also agree with activation energies measured by conventional stressing techniques and are in the same range as electromigration mechanisms originating from grain boundaries. Through the current dependence of γ, and the current dependence of the noise power magnitude, we attempted to predict electromigration damage and time-to-failure. For the first time, we incorporated the current dependence of the spectral form in the analysis of noise magnitude for electromigration.

Polycrystalline silicon films with relatively large grain size were obtained by aluminum-induced crystallization (AIC) of amorphous silicon films. Unlike conventional deposition techniques which require high temperatures, crystallization was accomplished by annealing at temperatures ranging from 475degC to 550degC, for 90 minutes. Polysilicon films thus obtained exhibited piezoresistive properties. XRD characterization of the film verified good polycrystalline structure. Electrical characterization of the film verified high conductivity polysilicon film thus eliminating further doping steps. The fabrication technique described here would be suitable for attaining polycrystalline silicon films on substrates or structures with stringent thermal budget constraints.

We performed 1ƒ noise measurements on n-channel Hg1−xCdxTe Metal-Insulator-Semiconductor Field-Effect Transistors (MISFETs) biased in linear and saturation regions of operation at 77 K. The cadmium mole fraction x was approximately 0.29 which corresponds to an energy band-gap of 0.24 eV at 77 K. Through the investigation of the dependence of drain voltage noise power spectral density on gate and drain bias, we estimated the insulator-semiconductor interface trap density as a function of energy. In this analysis, both the noise magnitude and the spectral shape was studied. The frequency span was from 150 Hz to 5 kHz. The noise behavior of the device was modeled using the modified McWhorter Model, originally developed for silicon FETs. The interface trap concentration values computed from the low-frequency noise measurements using the above model were found to agree closely with HgCdTeZnS interface properties measured by capacitance and conductance methods.

Low frequency noise (LFN) characteristics of HfSiO and HfSiON nMOS with TiN metal gate were compared. Two different methods to introduce nitrogen in HfSiO, plasma and thermal nitridation, were discussed from LFN point of view. Using Multi‐stack Unified Noise (MSUN) model, number and mobility fluctuation components were separated to find out the effects of processing on LFN characteristics. Different processing techniques have negligible effects on number fluctuation components. However, mobility fluctuation components were significantly affected. The reason might be due to the presence and distribution of various Coulomb scattering sites at the silicon‐high‐k interface and in the bulk of high‐k oxide due to different nitridation processes.

A pyroelectric infrared detector operating at room temperature and based on semiconducting Y-Ba-Cu-O was fabricated. The capacitor structure consisting of semiconducting Y-Ba-Cu-O layer sandwiched between two Nb electrodes was fabricated on top of a thermally isolated SiO2 bridge. The polycrystalline Y-Ba-Cu-O layer was deposited by ambient-temperature sputtering while standard Si micromachining techniques were used to etch the silicon under the oxide bridge. The pyroelectric response of the material is characterized by the temperature coefficient of polarization (p=dP/dT) which was measured to be as high as 65 nC/K cm2 without an externally applied electric field. The pyroelectric figure of merit Fd for the material was estimated to be 0.032 (cm3/J)1/2. Employing a radiometric infrared source, the room-temperature voltage responsivity RV and specific detectivity D* of the unbiased detector were measured to be over 103 V/W and 108 cm Hz1/2/W, respectively. This letter discusses the characteristics of this...

There have been recent innovations to reduce the cost of packaging for MEMS devices, without deteriorating their performance. One such novel design for device-level encapsulation (self-packaged) of uncooled infrared (IR) microbolometers is documented here. Device-level vacuum encapsulation has the potential to eliminate some major problems associated with the bolometer performance such as high thermal conductance of the ambient atmosphere, the high cost associated with conventional vacuum packaging, and the degradation of optical transmission at different wavelengths through a conventional package window. The device-level encapsulated bolometers can also be fabricated with flexible substrates, which have the advantage of conforming to non-planar surfaces compared to Si or other rigid substrates. In addition, a flexible superstrate with low shear stress has applications in robotics, aerospace, defense and biomedicine as a "Smart skin", a name given to multisensory arrays on conformal substrates to emulate human skin functions on inanimate objects. Self-packaged uncooled microbolometer arrays of 40x40 μm2 and 60x60 μm2 are fabricated on top of Si wafer with a sacrificial layer using semiconducting Yttrium Barium Copper Oxide (YBCO) as the infrared sensing material. A two-layer surface micromachining technique in conjunction with a resonant cavity and a reflecting mirror are used for the sensor structure. The devices have demonstrated voltage responsivities of 7.9x103 V/W with a temperature coefficient of resistance of -2.5% K-1, and thermal conductivity of 2.95x10-6 W/K. The device performance was similar in air and vacuum, demonstrating vacuum integrity and a good device-level encapsulation.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The flicker noise characteristics of MOSFETs with HfO2, HfAlOx, Al2O3 / HfO2 gate stacks have been studied, where both n and p type devices having 10 Å or 40 Å SiO2 interfacial layer (IFO) were considered. The corresponding equivalent oxide thickness (EOT) values were 23Å, 53Å for HfO2; 28.5Å, 58.5Å for HfAlOx; and 33Å, 63 Å for Al2O3 / HfO2. Gate leakage currents were (~ 2-5x10-5 A/cm2) which are 2 orders of magnitude lower compared to SiO2 devices with similar oxide thickness. The positive and negative threshold shifts as derived from the threshold voltages of n, p devices, respectively, suggested the presence of interface states between poly-gate and dielectric. Normalized power spectral density plot vs. gate overdrive shows that the devices with thin interfacial oxide (IFO) layer exhibit about an order of magnitude higher noise than those with thicker IFO owing to higher number of traps in the high-k and to the fact that carrier tunneling distance is ~20 Å. The Unified Model representing the carrier number and correlated mobility fluctuations was used to extract the oxide trap density and Coulomb scattering coefficient values. In general, n-type HfO2 devices yielded low noise, trap density and best mobility values compared to the other two gate stacks.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This paper presents progress made in making device-level vacuum-packaged microbolometers as infrared detectors on flexible substrates. Polyimide PI5878G serves as the flexible substrate and semiconducting yttrium barium copper oxide (YBCO) is used as the bolometric material. Finite element analysis is used to design a vacuum cavity housing a microbolometer. Suitable materials are selected for the microcavity fabrication based on results of the computer simulations. During fabrication, sacrificial polyimide around the detector facilitates the formation of a vacuum microcavity with an optical window. Micromachining is carried out through trenches in the microcavity wall. After isolating the microbolometer from the ambient, the trenches are sealed shut by sputtering in vacuum. The fabricated devices are characterized for responsivity and detectivity. At a bias voltage of 10 V, 40-40mu m2 devices exhibited a current responsivity of 6.13 timesl0-5 A/W to a broad-band infrared radiation modulated at 5 Hz. A maximum detectivity of 1.76times105 cm-Hz1/2/W was measured. A relatively low thermal conductance of 3.36times10-6 W/K was measured implying good thermal isolation of the bolometers and therefore an intact vacuum cavity

The effect of interfacial SiO2 layer resulting from Stress Relieved Pre‐Oxide (SRPO) treatment on the low frequency noise characteristics of TaSiN/HfO2 MOSFETs is studied. Noise comparison with near‐equivalent devices having a SiO2 interfacial layer from standard RCA process revealed better overall performance with the new process. Further analysis using the correlated mobility‐number fluctuations model yielded close values for the oxide trap density and a considerably different Coulomb scattering coefficient values. In general, SRPO oxide improved the device performance that is further made evident by the mobility values obtained from the split C‐V measurements.

One common requirement of microbolometers fabricated on both rigid and flexible substrates is the need for vacuum packaging to eliminate the thermal conductivity of air and achieve high performance. However, vacuum packaging of microbolometers is expensive and is a limiting factor in achieving truly low-cost uncooled infrared detection. Vacuum packing of microbolometers on flexible substrates requires a novel approach unless flexibility is to be sacrificed. This paper explores the vacuum packaging of microbolometers through self-packaging. In this case, the micromachined encapsulation in a vacuum cavity is investigated through computer simulation of microbolometers in flexible polyimide films and through the encapsulation of microbolometers on rigid Si substrates with a Si3N4 shell. In this manner, self packaged uncooled microbolometers were fabricated on a Si wafer with semiconducting yttrium barium copper oxide (YBCO) as the infrared sensing material. The self-packaged structure is designed such that it can be covered with a superstrate, yielding low stress in the flexible skin sensors and better detection figures of merit. The devices have demonstrated voltage responsivities over 103 V/W, detectivities above 106 cm Hz1/2/W and temperature coefficient of resistance around -3.3% K-1. Computer simulations using CoventorWare and MEMulator have been used to determine suitable materials for the process, the optimum design of a vacuum element and a streamlined process flow.

This paper presents work on micromachined infrared detectors on flexible substrates. The detectors are made of semiconducting yttrium-barium-copper-oxide (YBCO) and are built on a 40-50 /spl mu/m layer of polyimide (PI58578G) that serves as the flexible substrate. Two variants of micromachined infrared detectors have been fabricated The first variant employs a mesa structure in which self-supporting Ti arms hold up the detector pixel. The second variant has a more planar topology with the detector being supported by a layer of silicon nitride. Surface micromachining is used to isolate the detectors from the substrate. After fabrication the polyimide is peeled off the carrier wafer and the devices are packaged and characterized. The 40/spl times/40 /spl mu/m/sup 2/ microbolometers have responsivities ranging from 7.4/spl times/10/sup 3/ V/W to 10/sup 4/ V/W and detectivities ranging from 6.6/spl times/10/sup 5/ cm-Hz/sup 1/2//W to 10/sup 8/ cm-Hz/sup 1/2//W. These results are comparable to those obtained for devices made on a rigid silicon substrate. The effect of substrate heating is also investigated and found not to affect the detector performance.

This paper reports progress on the development of micromachined infrared microsensors on flexible polymer substrates. The flexible substrates were formed by spin-coating polyimide films (HD Microsystems PI-5878G) on silicon wafer carriers. Semiconducting Yttrium Barium Copper Oxide (YBCO) was used as the thermistor. The microbolometer was fabricated using a polyimide (HD Microsystems PI2737) sacrificial mesa and titanium electrode arms. The YBCO thermistor was suspended above the substrate by the electrode arms after the sacrificial layers have been removed by micromachining. The polyimide substrate was then removed from the silicon wafer carrier to complete the fabrication of the infrared microsensors on a flexible polyimide substrate. The measured thermal conductance of the microbolometers ranged from 9.07x10 -6 W/K for a non-micromachined to 4.0x10 -7 W/K for a micromachined sensor. As a result, the responsivity and detectivity were measured to be as high as 6.1x10 4 V/W and a 1.2x10 8 cmHz 1/2 /W, respectively, with a 970 nA current bias. This level of performance is comparable to similar micromachined detectors fabricated on silicon substrates.

A gated lateral bipolar transistor is a bulk lateral BJT in parallel with a MOSFET at the surface. The base current components such as surface recombination and space charge recombination currents are two of the dominant noise sources in the lateral BJT. If the gate is biased such that the MOSFET is in the off-state by accumulating carriers underneath the oxide in the base surface, the noise contribution by these two base current (Ib) components can be better understood. The carrier accumulation in the base surface can be modulated with different gate bias, which in turn will affect the fluctuation of the surface recombination current component. In this paper, noise power spectral density of gated lateral PNP transistors, fabricated in Texas Instruments Standard Bipolar Process, has been discussed. The base current noise power spectral density (SIb) was extracted from the cross-correlation noise spectrum measured between the base and the collector circuits for different gate biasing conditions. Based on the frequency exponent dependence of the noise power spectral density, it was found that the noise in the low frequency range is in the form of 1/f noise. S Ib was found to be the dominant noise source for these devices as the coherence between the base and collector power spectral density was very close to 1. S Ib was extracted for a base current range of 8 nA to 1microA for a gate bias range of 0V to 40V. The SPICE noise model parameters, AF and KF were also determined for each case from the dependence of S Ib on I b . The noise was measured on devices with different base width values.

We review performance and physical characteristics of yttrium barium copper oxide (YBCO) compound as an infrared (IR) photodetector. YBCO has been used as the IR detector material in both superconducting (oxygen-rich) and semiconducting (oxygen-depleted) phases. YBCO in its crystalline, Yba2Cu3O6+x phase with x>0.95 is a high-temperature superconducting material with the superconducting transition Tcapproximately equals 90K. The superconducting YBCOIR detectors operate as either nonequilibrium (quantum) or bolometric (thermal) devices. The nonequilibrium devices are characterized by very short, single-picosecond photoresponse times and are expected to find applications in optoelectronics and imaging, as well as ultrafast optical-to-electrical transducers for digital input applications. The bolometric mechanism results in relatively slow but very sensitive detectors with possible applications in astronomy. In addition to superconducting IR sensors, interest in uncooled YBCO devices is growing very rapidly. Despite somewhat lower sensitivity and significantly reduced speed of response, as compared to the superconducting counterpartners, the uncooled IR detectors are characterized by much lower operating cost and weight due to lack of cooling cryogens and are compatible with existing silicon-based processing and fabrication. The last point is of paramount importance if the IR-sensitive pixels are to be integrated with CMOS read-out circuitry for monolithic focal plane arrays and infrared cameras. Amorphous uncooled YBCO photodetectors operate as either photoconductive bolometers of unbiased pyroelectric devices.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Publisher Summary This chapter describes the performance and physical characteristics of yttrium barium copper oxide (YBaCuO) as an infrared (IR) detector. YBaCuO is the most studied and the best characterized material among the CuO-based high-temperature superconductors (HTS). Superconductive YBaCuO detectors can be operated in a bolometric mode near Tc, which is the critical transition temperature between the superconductive and nonsuperconductive states, utilizing the resistive transition or well below Tc, which uses the voltage response associated with changing the kinetic inductance of the supercurrent. Semiconducting YBaCuO has demonstrated potential as an uncooled IR detector operating with zero-bias as a micropyroelectric detector and voltage or current biased as a microbolometer. The room-temperature fabrication of semiconducting YBaCuO thin films by radio frequency (RF) magnetron sputtering is simple and compatible with CMOS substrates for the production of focal plan arrays. Compatibility is achieved with the use of micromachining techniques and a conventional polyimide sacrificial layer to produce thermal isolation structures. Superconducting YBaCuO is discussed in the chapter with prospects for applications in both quantum and thermal IR detection schemes. A brief review of the other commonly used nonsuperconducting IR detector materials is also included in the chapter.

We measured low‐frequency noise and temperature coefficient of resistance β=(dR/dT)/R on YBa2Cu3O7−δ thin films at varying temperatures around superconducting transition. Magnetic field densities of 18–88 G were applied to the films. We found Tc to decrease slightly with magnetic field even though β at the respective Tc remained constant. At the superconducting transition, the voltage noise power spectral density over the 10–1000 Hz frequency range decreased with magnetic field, whereas no change in noise behavior was observed with varying the magnetic field in normal state. At a constant temperature in transition, as the magnetic field density was varied, the noise magnitude followed the β2 dependence as predicted by the local thermal fluctuations theory of 1/f noise.

This paper reports the fabrication of microbolometers using semiconducting YBaCuO as the IR sensing material. The detectors are operable at room temperature and thus are suitable for lost-cost and high performance imaging applications. Semiconducting YBaCuO is promising as a bolometric material as it has a thermal coefficient of resistance near 3% and relatively low noise. Two different bolometer structures will be reported here. First generation YBaCuO microbolometers were built on micromachined SiO 2 bridges using wet etching techniques to undercut the silicon. The second generation structures were processed upon micromachined Si 3 N 4 membranes with sputtered MgO films used as sacrificial layers. The membrane structures are the first of its kind to incorporate MgO as a sacrificial layer, and they offer a fabrication technique that is fully CMOS compatible, with all processing at ambient temperatures. Detectivities in the order of 10 8 cm Hz 1/2 /W were measured at 30 Hz chopping frequency in both structures. The thermal conductance of the suspended membranes was on the order of 10 -7 W/K, which is desirable as low thermal conductance yields high responsivities. There are realizable optimizations for both applications to yield detectivities over 10 9 cm Hz 1/2 /W. All measurements reported here were performed at ambient temperature with no temperature stabilization.

Nanoimprint lithography is emerging as a viable contender for fabrication of large-scale arrays of 5–500 nm features. A fabrication process for the realization of thin nanoporous membranes using thermal nanoimprint lithography is presented. Suspended silicon nitride membranes were fabricated by low-pressure chemical vapor deposition (LPCVD) in conjunction with a potassium hydroxide-based bulk micromachining process. Nanoscale features were imprinted into a commercially available thermoplastic polymer resist using a prefabricated silicon mold. The pattern was reversed and transferred to a thin aluminum oxide layer by means of a novel two-stage lift-off technique. The patterned aluminum oxide was used as an etch mask in a CHF3/He-based reactive ion etch process to transfer the pattern to silicon nitride. Highly directional etch profiles with near vertical sidewalls and excellent Si3N4/Al2O3 etch selectivity were observed. One micrometer thick porous membranes with varying dimensions of 250 × 250 µm2 to 450 × 450 µm2 and a pore diameter of 400 nm have been engineered and evaluated. Results indicate that the membranes have consistent nanopore dimensions and precisely defined porosity, which makes them ideal as gas exchange interfaces in blood oxygenation systems as well as other applications such as dialysis.

Nitrided hafnium silicate is the leading candidate for possible replacement of SiON as a gate dielectric. 1/f noise characteristics of plasma and thermally nitrided Hf-based high-dielectric constant (high-k) gate dielectrics were investigated. Plasma nitrided samples showed less noise than thermally nitrided samples. The mobility fluctuation component of 1/f noise was found to show a strong process dependence, specifically on the nitridation technique. Increase in the number of Coulomb scattering sites due to the additional Si–N bonds near the high-k/Si interface is suggested as the reason for this dependence. This work represents the first investigation on the effect of different nitridation methodologies on low-frequency noise mechanisms in ultrathin (∼2 nm) Hf-based high-k nMOSFET (metal-oxide-semiconductor field effect transistor).

The origin of 1∕f fluctuations in positive-negative-positive (PNP) polycrystalline silicon-emitter bipolar-junction transistors is described. The interfacial oxide (IFO) at the monosilicon–polycrystalline silicon interface is found to significantly affect the noise behavior. The low-frequency noise originates from two independent fluctuation mechanisms: in the diffusion and tunneling components of the base current noise power spectral density (SIB) and from the diffusion current and carrier number fluctuations in the collector current noise power spectral density (SIC). The Hooge noise parameters for electrons and holes are calculated from the diffusion fluctuation models for SIB and SIC, respectively. Noise measurements on devices with different sizes and different IFO thicknesses indicate that the fluctuations occur in the minority-carrier (electron) tunneling current component of SIB through the IFO. The thickness of the IFO is estimated using this noise model. The tunneling fluctuations dominate over ...

The pyroelectricity and crystallization level of yttrium barium copper oxide (YBa2Cu3O6+x) thin films have been investigated by depositing the thin films by rf magnetron sputtering at different substrate temperatures. A portion of the thin film samples were analyzed by x-ray diffraction (XRD) to investigate the crystallinity while the remainder were processed to fabricate capacitor structures with Au electrodes to study the pyroelectric properties of the thin films. We observed different crystallization levels for samples that were deposited at different substrate temperatures. Pyroelectric behavior was observed to be correlated to the strength of the XRD peaks observed. Samples that lack crystallinity did not display pyroelectric behavior, while samples with observable crystallinity displayed pyroelectric behavior, either as deposited without poling or induced by poling. Samples lacking crystallinity could not be poled to display a measurable pyroelectric behavior. Pyroelectric coefficients on the order of 50 nC/K cm2 were observed in the polycrystalline samples.