50-nm fully depleted SOI CMOS technology with HfO/sub 2/ gate dielectric and TiN gate

In this paper, we demonstrate for the first time CMOS thin-film metal gate FDSOI devices using HfO/sub 2/ gate dielectric at the 50-nm physical gate length. Symmetric V/sub T/ is achieved for long-channel nMOS and pMOS devices using midgap TiN single metal gate with undoped channel and high-k dielectric. The devices show excellent performance with a I/sub on/=500 /spl mu/A//spl mu/m and I/sub off/=10 nA//spl mu/m at V/sub DD/=1.2 V for nMOSFET and I/sub on/=212 /spl mu/A//spl mu/m and I/sub off/=44 pA//spl mu/m at V/sub DD/=-1.2 V for pMOSFET, with a CET=30 /spl Aring/ and a gate length of 50 nm. DIBL and SS values as low as 70 mV/V nand 77 mV/dec, respectively, are obtained with a silicon film thickness of 14 nm. Ring oscillators with 15 ps stage delay at V/sub DD/=1.2 V are also realized.     

Electric fields within cells as a function of membrane resistivity--a model study

Externally applied electric fields play an important role in many therapeutic modalities, but the fields they produce inside cells remain largely unknown. This study makes use of a three-dimensional model to determine the electric field that exists in the intracellular domain of a 10-/spl mu/m spherical cell exposed to an applied field of 100 V/cm. The transmembrane potential resulting from the applied field was also determined and its change was compared to those of the intracellular field. The intracellular field increased as the membrane resistance decreased over a wide range of values. The results showed that the intracellular electric field was about 1.1 mV/cm for R/sub m/ of 10 000 /spl Omega//spl middot/cm/sup 2/, increasing to about 111 mV/cm as R/sub m/ decreased to 100 /spl Omega//spl middot/cm/sup 2/. Over this range of R/sub m/ the transmembrane potential was nearly constant. The transmembrane potential declined only as R/sub m/ decreased below 1 /spl Omega//spl middot/cm/sup 2/. The simulation results suggest that intracellular electric field depends on R/sub m/ in its physiologic range, and may not be negligible in understanding some mechanisms of electric field-mediated therapies.     

Influence of spinel substrate and over-layer for enhanced SAW and AO properties with KNbO3 thin film

Surface acoustic wave (SAW) propagation characteristics have been studied using modeling calculations for a potassium niobate (KNbO/sub 3/) thin film-layered structure with [001] and [110] orientation on a single crystal spinel (MgAl/sub 2/O/sub 4/) substrate, and a spinel buffer layer on silicon. Variation in the electromechanical coupling and acoustic attenuation has been compared. A significantly high value of coupling factor (k/sub max//sup 2/=23%) is obtained for the [001]KNbO/sub 3//spinel structure by introducing an optimum thickness of spinel over-layer for potential wide bandwidth SAW device applications. The dispersion characteristics with the [110] KNbO/sub 3/ orientation indicate an initial peak in the coupling coefficient value (k/sub max//sup 2/=8.8%) at a relatively low KNbO/sub 3/ film thickness that appears attractive for fabricating devices with thinner films. The KNbO/sub 3/ film with [001] orientation is found attractive for efficient acousto-optic (AO) device application with the formation of a symmetric waveguide structure (spinel(0.5 /spl mu/m)/KNbO/sub 3/(1.0 /spl mu/m)/spinel). A high value of k/sup 2/=23.5% with 50% diffraction efficiency has been obtained for the spinel(0.5 /spl mu/m)/KNbO/sub 3/(1.0 /spl mu/m)/spinel structure at 1 GHz SAW frequency and 633 nm optical wavelength at a very low input drive power of 15.4 mW.     

Development and analysis of a PCB vector 2-D magnetic field sensor system for electronic compasses

A high-sensitivity vector two-dimensional (2-D) magnetic sensor system for low magnetic field measurements has been realized and tested. The system, made in PCB technology, consists of a double-axis Fluxgate magnetic sensor and the readout electronic circuitry, based on second-harmonic detection. The amorphous magnetic materials Vitrovac 6025X (25 /spl mu/m thick) and Vitrovac 6025Z (20 /spl mu/m thick) were used as the ferromagnetic core of the sensor. By applying a sinusoidal excitation current having a 450-mA peak at 10 kHz with Vitrovac 6025Z, the measured magnetic sensitivity was about 1.25 mV//spl mu/T. This value seems to be adequate for the Earth's magnetic field detection (/spl plusmn/60 /spl mu/T). The full-scale linearity error was about 1.5%. By using the thicker Vitrovac 6025X and a sinusoidal excitation current having a 600-mA peak at 10 kHz, a maximum sensitivity of approximately 1.68 mV//spl mu/T with a linearity error of about 1.55% full scale in the range of /spl plusmn/60 /spl mu/T were measured. Due to the use of commercially available ferromagnetic materials, the vector 2-D magnetic sensor system presented is characterized by a very simple fabrication process, thus allowing low-cost devices to be designed.     

Benchmarking nanotechnology for high-performance and low-power logic transistor applications

Recently there has been tremendous progress made in the research of novel nanotechnology for future nanoelectronic applications. In particular, several emerging nanoelectronic devices such as carbon-nanotube field-effect transistors (FETs), Si nanowire FETs, and planar III-V compound semiconductor (e.g., InSb, InAs) FETs, all hold promise as potential device candidates to be integrated onto the silicon platform for enhancing circuit functionality and also for extending Moore's Law. For high-performance and low-power logic transistor applications, it is important that these research devices are frequently benchmarked against the existing Si logic transistor data in order to gauge the progress of research. In this paper, we use four key device metrics to compare these emerging nanoelectronic devices to the state-of-the-art planar and nonplanar Si logic transistors. These four metrics include: 1) CV/I or intrinsic gate delay versus physical gate length L/sub g/; 2) energy-delay product versus L/sub g/; 3) subthreshold slope versus L/sub g/; and 4) CV/I versus on-to-off-state current ratio I/sub ON//I/sub OFF/. The results of this benchmarking exercise indicate that while these novel nanoelectronic devices show promise and opportunities for future logic applications, there still remain shortcomings in the device characteristics and electrostatics that need to be overcome. We believe that benchmarking is a key element in accelerating the progress of nanotechnology research for logic transistor applications.     

High-frequency performance projections for ballistic carbon-nanotube transistors

A quasi-static approach is combined with a theory of ballistic nanotransistors to assess the high-frequency performance potential of carbon-nanotube field-effect transistors. A simple equivalent circuit, which applies in the ballistic limit of operation, is developed for the intrinsic device, and then employed to determine the behavior of the unity-current-gain frequency (f/sub T/) with gate voltage. The circuit is shown to reduce to the expected forms in the so-called "MOS" and "bipolar" limits. The f/sub T/ is shown to approach a maximum value of v/sub F//2/spl pi/L/spl ap/130 GHz/L (/spl mu/m) at high gate voltage, where v/sub F/ is the nanotube's Fermi velocity and L is the channel length, and to fall at low gate voltage due to the presence of source and drain electrostatic capacitances. The impact of the gate electrostatic capacitance on the f/sub T/ is also discussed. Numerical simulations on a "MOSFET-like" or "bulk-switched" carbon-nanotube transistor are shown to support the conclusions.     

Development and comparative analysis of fluxgate magnetic sensor structures in PCB technology

In this paper, we present a family of fluxgate magnetic sensors on printed circuit boards (PCBs), suitable for an electronic compass. This fabrication process is simple and inexpensive and uses commercially available thin ferromagnetic materials. We developed and analyzed the prototype sensors with software tools based on the finite-element method. We developed both singleand double-axis planar fluxgate magnetic sensors as well as front-end circuitry based on second-harmonic detection. Two amorphous magnetic materials, Vitrovac 6025X (25 /spl mu/m thick) and Vitrovac 6025Z (20 /spl mu/m thick), were used as the ferromagnetic core. We found that the same structures can be made with Metglas ferromagnetic core. The double-axis fluxgate magnetic sensor has a sensitivity of about 1.25 mV//spl mu/T with a linearity error of 1.5% full scale, which is suitable for detecting Earth's magnetic field (/spl plusmn/60 /spl mu/T full-scale) in an electronic compass.     

Spin-transfer switching current distribution and reduction in magnetic tunneling junction-based structures

Spin transfer switching current distribution within a cell and switching current reduction were studied at room temperature for magnetic tunnel junction-based structures with resistance area product (RA) ranged from 10 to 30 /spl Omega/-/spl mu/m/sup 2/ and TMR of 15%-30%. These were patterned into current perpendicular to plane configured nanopillars having elliptical cross sections of area /spl sim/0.02 /spl mu/m/sup 2/. The width of the critical current distribution (sigma/average of distribution), measured using 30 ms current pulse, was found to be 3% for cells with thermal factor (KuV/k/sub B/T) of 65. An analytical expression for probability density function p(I/I/sub c0/) was derived considering a thermally activated spin transfer model, which supports the experimental observation that the thermal factor is the most significant parameter in determining the within-cell critical current distribution. Spin-transfer switching current reduction was investigated through enhancing effective spin polarization factor /spl eta//sub eff/ in magnetic tunnel junction-based dual spin filter (DSF) structures. The intrinsic switching current density (J/sub c0/) was estimated by extrapolating experimental data of critical current density (J/sub c/) versus pulse width (/spl tau/), to a pulse width of 1 ns. A reduction in intrinsic switching current density for a dual spin filter (DSF: Ta/PtMn/CoFe/Ru/CoFeB/Al2O3/CoFeB/spacer/CoFe/PtMn/Ta) was observed compared to single magnetic tunnel junctions (MTJ: Ta/PtMn/CoFe/Ru/CoFeB/Al2O3/CoFeB/Ta). J/sub c/ at /spl tau/ of 1 ns (/spl sim/J/sub c0/) for the MTJ and DSF samples were 7/spl times/10/sup 6/ and 2.2/spl times/10/sup 6/ A/cm/sup 2/, respectively, for identical free layers. Thus, a significant enhancement of the spin transfer switching efficiency is seen for DSF structure compared to the single MTJ case.     

Limiting sensitivity of a differential absorption spectrometer with direct detection in the 2/spl nu//sub 3/ and /spl nu//sub 2/+2/spl nu//sub 3/ vibration bands [methane detection applications]

A differential absorption spectrometer, for methane detection, using tunable laser diodes in the 1.33-/spl mu/m and 1.66-/spl mu/m bands, has been studied. The spectral scanning is carried out by current modulation of the laser diode. We analyzed the performance with a multimode Fabry-Perot laser diode in the /spl nu//sub 2/+2/spl nu//sub 3/ band of methane and a monomode laser diode in the 2/spl nu//sub 3/ band. The theoretical results are validated by several experiments. To determine the sensitivity limit of the sensor, we have examined the influence of the noise sources. A sensitivity of 10 ppm/spl middot/m was obtained in the 2/spl nu//sub 3/ band. The main limiting factors are the relative intensity noise of the laser, optical interferences, and quantization noise. We also analyzed the influence of the temperature on the laser diode emission spectra and the methane absorption spectra.     

Amorphous silicon two-color microbolometer for uncooled IR detection

This paper describes the modeling and design of two-color microbolometers for uncooled infrared (IR) detection. The goal is to develop a high resolution IR detector array that can measure the actual temperature and color of an object based on two spectral wavelength regions. The microbolometer consists of high temperature amorphous silicon (a-Si:H) thin film layer held above the substrate by Si/sub 3/N/sub 4/ bridge. A thin NiCr absorber with sheet resistance of 377 /spl Omega//sqr is used to enhance the optical absorption in the medium and long IR wavelength windows. A tunable micromachined Al-mirror was suspended underneath the detector. The mirror is switched between two positions by the application of an electrostatic voltage. The switching of the mirror between the two positions enables the creation of two wavelength response windows, 3-5 and 8-12 /spl mu/m. A comparison of the two response wavelength windows enables the determination of the actual temperature of a viewed scene obtained by an IR camera. The microbolometer is designed with a low thermal mass of 1.65/spl times/10/sup -9/ J/K and a low thermal conductance of 2.94/spl times/10/sup -7/ W/K to maximize the responsivity R/sub v/ to a value as high as 5.91/spl times/10/sup 4/ W/K and detectivity D/sup */ to a value as high as 2.34/spl times/10/sup 9/ cm Hz/sup 1/2//W at 30 Hz. The corresponding thermal time constant is equal to 5.62 ms. Hence, these detectors could be used for 30-Hz frame rate applications. The extrapolated noise equivalent temperature difference is 2.34 mK for the 8-12 /spl mu/m window and 23 mK for the 3-5 /spl mu/m window. The calculated absorption coefficients in the medium and long IR wavelength windows before color mixing are 66.7% and 83.7%. However, when the color signals are summed at the output channel, the average achieved absorption was 75%.     

Interaction between magnetoresistor and magnetotransistor in the longitudinal and folded vertical Hall devices

This study investigates the one-dimensional longitudinal and folded vertical Hall devices, fabricated in a standard 0.35-/spl mu/m CMOS process. The smallest nonlinearity error 0.18%, the minimum offset 0.29 mV, and the maximum supply-current-related sensitivity S/sub RI/=3.837 V/A/spl middot/T, are obtained with a 10-mA bias current excited by the supply voltage of 0.6 V. The main magnetic mechanism is that the filament current of the vertical magnetoresistor is directly injected into the base region of the bulk magnetotransistor (BMT) to increase the density of minority carriers and then enhance the magnetosensitivity. Furthermore, the induced Hall voltage of the longitudinal vertical Hall device is proportional to the bias current, but the folded vertical Hall device is inversely impacted. This advantage makes it possible to get a low-power folded vertical Hall device. The folded style not only reduces the nonlinearity error but also minimizes the offset. Unfortunately, the tradeoff is a fall in sensitivity. The BMT is applied to increase magnetic sensitivity and to compensate for this negative impact.     

Inspection of intrinsic critical currents for spin-transfer magnetization switching

We examined the relationships between critical current, I/sub c/, and switching time, /spl tau//sub p/, for spin-transfer switching in two regions: (region I) /spl tau//sub p//spl Gt//spl tau//sub 0/, where thermal switching is accompanied and (region II) /spl tau//sub p/< several tens times /spl tau//sub 0/, where /spl tau//sub 0/ is the attempt time for thermal switching (/spl ap/1 ns). We estimated I/sub c0/, defined as the intrinsic I/sub c/ at 0 K, for both regions and confirmed experimentally that those I/sub c0/ coincided with each other at room temperature (RT). The value of I/sub c/ at /spl tau//sub p/=1 ns, measured with microwaves, was approximately 1.6 times the I/sub c0/. This suggested that we use at least two times I/sub c0/ as the writing currents of magnetic memory devices for nsec spin-transfer switching at RT. Although I/sub c0/ for both regions were defined as I/sub c/ at 0 K (I/sub c//sup 0K/) in theory, they showed temperature dependence at low temperatures; |I/sub c0/| for region I increased with decreasing temperature, and the estimated I/sub c//sup 0K/ was approximately three times I/sub c0/ for RT. This temperature dependence was quite different from that for region II.     

Design and fabrication of a novel crystal SiGeC far infrared sensor with wavelength 8-14 micrometer

In this paper, we report the design, fabrication, and performance of a novel crystal SiGeC infrared sensor with wavelength 8-14 /spl mu/m by bulk micromachining technology for portable far infrared ray (FIR) in rehabilitation system application. The working principle of the sensor is based on the change of thermistor's resistance under the irradiation FIR light. The thermistor in the IR detector is made of Si/sub 0.68/Ge/sub 0.31/C/sub 0.01/ thin films for its large activation energy of 0.21 ev and the temperature coefficient (TCR) of -2.74%, respectively. Finite element method package ANSYS has been employed for analyze of the thermal isolation and stress distribution in the IR detector. The dimension of the microbridge fabricated by anisotropic wet etching is 2000 /spl times/ 2000 /spl times/ 25 /spl mu/m/sup 3/. The developed FIR sensor exhibits the thermal conductance of 1.85 /spl times/ 10/sup -1/ WK/sup -1/ and the heat capacity as 7.4 /spl times/ 10/sup -7/ JK/sup -1/ under air ambient at room temperature. The responsivity is 523 VW/sup -1/ in the waveband 8-14 /spl mu/m with nickel absorber under a bias voltage 1.5 V.     

Field-emission triode of low-temperature synthesized ZnO nanowires

A field-emission triode based on the low-temperature (75/spl deg/C) and hydrothermally synthesized single-crystalline zinc-oxide nanowires (ZnO NWs) grown on Si substrate with a silicon dioxide (SiO/sub 2/) insulator was fabricated for the controllable field-emission device application. Field-emission measurement reveals that the ZnO NWs fabricated on the Si substrate exhibit a good emission property with the turn-on electric field and threshold electric field (current density of 1 mA/cm/sup 2/) of 1.6 and 2.1 V//spl mu/m, respectively, with a field enhancement factor /spl beta/ of 3340. The field-emission properties of the ZnO NW-based triode exhibit the controllable characteristics. The well-controlled field-emission characteristics can be divided into three parts: gate leakage region, linear region, and saturation region. Therefore, this study provides a low-temperature field-emission triode fabrication process that is compatible with the Si-based microelectronic integration, and the field-emission measurements also reveal that the emission behavior can be well controlled by adopting the triode structure.     

Unidirectional SAW transducer for gigahertz frequencies

A single-phase unidirectional transducer (SPUDT) structure using /spl lambda//4 and wider electrodes is introduced. The considerable difference between the reflectivity of short-circuited /spl lambda//4 electrodes and that of floating /spl lambda//2-wide electrodes on 128/spl deg/ lithium niobate (LiNbO/sub 3/) is exploited. The surface acoustic wave (SAW) device operating at 2.45 GHz has critical dimensions of about 0.4 /spl mu/m, accessible for standard optical lithography.     

The enhancement of Q factor for patterned ground shield inductors at high temperatures

We report on an effective way of using a patterned ground shield (PGS) to enhance the Q factor of on-chip spiral inductors. We fabricated PGS inductors using both 0.18 /spl mu/m and 0.35 /spl mu/m CMOS processes, with M1 and poly strip PGSs, respectively. The strip width and spacing of the PGSs are W/sub g/=0.8 /spl mu/m and S/sub g/=0.45 /spl mu/m, with metal thicknesses of t/sub p/={0.54,0.2} /spl mu/m in the 0.18 /spl mu/m process, and t/sub p/={0.6,0.3} /spl mu/m in the 0.35 /spl mu/m process. The separation distance D between PGS and top metal layer is different in both processes. We found that the Q factor degradation of inductors at high temperatures can be effectively compensated by using PGS. Among all geometric parameters of a PGS in the 0.18 /spl mu/m process, the parameter D is the critical factor for the shielding effectiveness, and M1 PGS is much more efficient than poly strip PGS in improving the inductor performance over the temperature range of 298 K to 358 K. However, in the 0.35 /spl mu/m process the latter is better than the former.     

Nonelectrical poling in ferroelectric polythioureas

A new poling method utilizing the cooperativity and strong hydrogen bonding force of thiourea groups is proposed in ferroelectric polythioureas [poly(octamethylene thiourea) and poly(nonamethyleno thiourea)]. The method, which is named "surface energy poling," takes advantage of the surface energy difference of the polar amorphous material to form remanent polarization. A polythiourea film sandwiched between a metal with higher surface energy and polytetrafluoroethylenes with lower surface energy was heated up to T/sub c/ [1.15/spl times/T/sub g/ (glass transition temperature)] and cooled slowly to room temperature. The resulting film showed a pyroelectric constant of 10 /spl mu//m/sup 2/K, giving evidence of remanent polarization. This method is similar to the orientation process in liquid crystal devices.     

Multidimensional CMOS in-plane stress sensor

This paper reports a novel multidimensional complementary metal-oxide semiconductor (CMOS) based stress sensor. The device uses an octagonal n-well in a p-substrate and eight peripheral contacts enabling the current to be switched in eight directions rotated by an angle of /spl pi//4. By taking full advantage of the piezoresistive behavior of single-crystal silicon, the measurement of all in-plane stress tensor components, i.e., /spl sigma//sub xx/, /spl sigma//sub yy/, and /spl sigma//sub xy/, is demonstrated. This information is derived from the zeroth and second angular-order Fourier components of voltage signals parallel and perpendicular to the switched current. Nonlinearities of the system are reduced by proper bias conditions using a center contact. The device was calibrated by applying defined normal stresses using a bending bridge setup. The device behavior was modeled including piezoresistive effects and the junction field effect by a combination of the finite element method and a nonlinear simulation program with integrated circuits emphasis (SPICE) network simulation using junction field effect transistor (JFET) elements. Stress sensitivities of 200 /spl mu/V V/sup -1/ MPa/sup -1/ are demonstrated for the determination of the three stress components.     

Design, optimization, and performance analysis of new photodiode structures for CMOS active-pixel-sensor (APS) imager applications

The dark current in the active-pixel-sensor (APS) cell of a CMOS imager is known to be mainly generated in the regions of bird's beak after the local oxidation of silicon process as well as the surface damage caused by the implantation of high doping concentration. Furthermore, shallow and deep pn-junctions can improve the photo-sensitivity for light of short and long wavelengths, respectively. In this paper, two new photodiode structures using p-substrate and lightly-doped sensor implant SN- as pn-junction photodiode with the regions of bird's beak embraced by SN- and p-field implants, respectively, are proposed and analyzed to reduce dark current and enhance the overall spectral response. 5 /spl mu/m/spl times/5 /spl mu/m APS cells fabricated in a 0.35-/spl mu/m single-poly-triple-metal (1P3M) 3.3-V CMOS process are designed by using the proposed photodiode structures. As shown from the experimental results, the two proposed photodiode structures of 5 /spl mu/m/spl times/5 /spl mu/m APS cells have lower dark currents of 30.6 mV/s and 35.2 mV/s at the reverse-biased voltage of 2 V and higher spectral response, as compared to the conventional structure and other photodiode structures. Thus, the two proposed new photodiode structures can be applied to CMOS imager systems with small pixel size, high resolution, and high quality.