V2O4-PEPC composite based pressure sensor

In this study, V₂O₄-PEPC based pressure sensor was designed and fabricated by drop-casting the blend of V₂O₄-PEPC microcomposite thin films of vanadium oxide (V₂O₄) micropowder (10 wt.%) and poly-N-epoxypropylcarbazole, PEPC (2 wt.%) in benzol (1 ml) on steel substrates. The thickness of the V₂O₄-PEPC films was in the range of 20-40 μm. The DC resistance of the sensor was decreased in average by 24 times as the pressure was increased up to 11.7 kNm⁻². The resistance-pressure relationships were simulated.     

A Novel Mesoporous CaO‐Loaded In2O3 Material for CO2 Sensing

A mesoporous CaO‐loaded In₂O₃ material (with Ca/In₂O₃ ratios ranging from 2.5 to 8.5 at %) has been synthesized and used as resistive gas sensor for the detection of CO₂. A nanostructured In₂O₃ matrix has been obtained by hard template route from the SBA‐15 silica template. Additive presence does not distort the lattice of In₂O₃, which crystallizes in the Ia3 cubic space group. It has been proved by XRD, HRTEM, Raman and XPS measurements that samples contain not only CaO but also CaCO₃ in calcite phase as a consequence of CaO carbonation. Pure In₂O₃ based sensors are low sensitive to CO₂, whereas those containing the additive show an important response in the 300–5000 ppm range of gas concentrations. As seen by DRIFTS, the electrical response arises from the interaction between CO₃^2– and CO₂, yielding bicarbonates products. The reaction is water‐assisted, so that hydration of the sensing material ensures sensor reliability whilst its dehydration would inhibit sensor response. The use of CaCO₃ instead of CaO does not cause significant differences in electrical and DRIFTS data, which corroborates the important role played by carbonate species in the sensing mechanism.     

Study on TiO2-doped ZnO thick film gas sensors enhanced by UV light at room temperature

The gas-sensing properties of titanium oxide (TiO₂)-doped zinc oxide (ZnO) thick film sensor specimens to typical ethanol vapor under UV light activation at room temperature have been investigated. Zinc nanoparticles were mixed with commercial TiO₂ in various weight percentage (0%, 1%, 5%, and 10%) and sintered at 650 °C for 2 h to prepare the thick film sensors. The sensors exhibit better photosensitivity and gas sensitivity to ethanol analyte. The response and recovery times are within 8 s. TiO₂ doping can improve the sensors stability and reproducibility. X-ray diffraction (XRD) and scanning electron microscopy (SEM) characterization of the film materials revealed that Zn₂TiO₄ and TiO₂ phases hindered the rod- or needle-like structure growth and subsequently affected the gas sensitivity. UV absorption spectra of the sensing film material completely dispersed in ethanol solution exhibited that the red shifts were caused with the doping of a small amount of TiO₂ into ZnO then blue shift was caused with higher TiO₂ level. The results of the UV spectra are well consistent with the photosensitive performance. The maximum sensitivity can be achieved by doping the amount of TiO₂ (5 wt%).     

New ISFET interface circuit design with temperature compensation

An integrated and new interface circuit with temperature compensation has been developed to enhance the ISFET readout circuit stability. The bridge-type floating source circuit suitable for sensor array processing has been proposed to maintain reliable constant drain-source voltage and constant drain current (CVCC) conditions for measuring the threshold voltage variation of ISFET due to the corresponding hydrogen ion concentration in the buffer solution. The proposed circuitry applied to Si₃N₄ and Al₂O₃-gate ISFETs demonstrate a variation of the drain current less than 0.1 μA and drain-source voltage less than 1 mV for the buffer solutions with the pH value changed from 2 to 12. In addition, the scaling circuitry with the V_T temperature correction unit (extractor) and LABVIEW software are used to compensate the ISFET thermal characteristics. Experimental results show that the temperature dependence of the Si₃N₄-gate ISFET sensor improved from 8 mV/°C to less than 0.8 mV/°C.     

Molecular relaxation temperature effects on emission efficiency of Organic Light-Emitting Diodes

This paper reports the influence of the molecular relaxation temperature and electric field on the emission efficiency of poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene-vinylene] (MEH-PPV) in Organic Light-Emitting Diode (OLED) structure. We observe that the photoluminescence (PL) depends on the OLED polarization (forward and reverse) and on MEH-PPV molecular β-relaxation (T_β ∼ 220 K) and α-relaxation (T_α ∼ 330 K) temperatures. Above T_β unbalance in charge carrier concentration in the device have a significant effect on the emission efficiency. The exciton energy transfer as a function of the sample temperature was determined using emission ellipsometry within the Stokes’ theory scope. Regardless of the OLED voltage polarization, the emission is partially linearly polarized and the polarization degree decreases significantly above T_β and T_α temperatures. Finally, we propose an approach to enhance the emission efficiency of luminescence polymers by controlling the molecular relaxation temperatures of the multilayer polymer OLEDs.     

LKE and BGI Lorentzian noise in strained and non-strained tri-gate SOI FinFETs with HfSiON/SiO2 gate dielectric

The LKE (Linear Kink Effect) and BGI (Back-Gate-Induced) Lorentzians present in the drain current noise spectra of fully-depleted tri-gate n- and pFinFETs, fabricated on sSOI and SOI substrates with HfSiON/SiO₂ gate dielectric are described.It is shown that the analysis of the parameters of LKE and BGI Lorentzians allows to find the values of (С_eq/m′β²), β and [j_EVB/(m′β)²] where С_eq is the body-source capacitance, m′ ≈ 1, β is the body factor and j_EVB is the density of the EVB current flowing through the gate dielectric.As a result, the following effects were observed for the first time: (i) (С_eq/m′β²) decreases with increasing gate overdrive voltage |V^∗| and depends sub-linearly on the effective fin width W_eff under strong inversion conditions; (ii) in depletion and weak inversion where (С_eq/β²) is independent of |V^∗| the proportionality (С_eq/β²) ∝ W_eff is observed for an effective width W_eff ? 0.87 μm while (С_eq/β²) becomes independent on W_eff for W_eff < 0.87 μm; (iii) the value of β for the FinFETs investigated is higher than for their planar counterparts; (iv) in spite of the fact that strain affects the barrier height at the Si/SiO₂ interface, the EVB current densities j_EVB for sSOI and SOI devices are equal; (v) the values of j_EVB for the HfSiON/SiO₂-devices are much higher than for the HfО₂/SiO₂-ones studied previously. It is also shown that the gate overdrive voltage |V^∗| at which the LKE Lorentzians start to appear is as low as 0.25 V.     

Long-term stability of Ni-silicide ohmic contact to n-type 4H-SiC

The thermal stability of Ni₂Si/n-SiC ohmic contacts with Au overlayer without or with Ta-Si-N diffusion barrier was investigated after long anneals at 400 °C in air. Current-voltage characteristics, sheet resistance measurements, Rutherford backscattering spectrometry, X-ray diffraction and scanning electron microscopy were used to characterize the contacts before and after aging. It is shown that aging of Au/Ni₂Si/n-SiC contact at 400 °C for 50 h resulted in electrical failure, as well as complete contact degradation for 150 h due to interdiffusion/reaction processes in the contact. The Au/Ta₃₅Si₁₅N₅₀/Ni₂Si/n-SiC contact is thermally stable after 150 h of aging at 400 °C and has great potential for use in SiC-based devices for high-temperature operation.     

High performance TaYOx-based MIM capacitors

TaYO_x-based metal-insulator-metal (MIM) capacitors with excellent electrical properties have been fabricated. Ultra-thin TaYO_x films in the thickness range of 15-30 nm (EOT ∼ 2.4-4.7 nm) were deposited on Au/SiO₂ (100 nm)/Si (100) structures by rf-magnetron co-sputtering of Ta₂O₅ and Y₂O₃ targets. TaYO_x layers were characterized by X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray (EDX) and X-ray diffraction (XRD) to examine the composition and crystallinity. An atomic percentage of Ta:Y = 58.32:41.67 was confirmed from the EDX analysis while XRD revealed an amorphous phase (up to 500 °C) during rapid thermal annealing. Besides, a high capacitance density of ∼3.7-5.4 fF/μm² at 10 kHz (ε_r ∼ 21), a low value of VCC (voltage coefficients of capacitance, α and β) have been achieved. Also, a highly stable temperature coefficient of capacitance, TCC has been obtained. Capacitance degradation phenomena in TaYO_x-based MIM capacitors under constant current stressing (CCS at 20 nA) have been studied. It is observed that degradation depends strongly on the dielectric thickness and a dielectric breakdown voltage of 3-5 MV/cm was found for TaYO_x films. The maximum energy storage density was estimated to be ∼5.69 J/cm³. Post deposition annealing (PDA) in O₂ ambient at 400 °C has been performed and further improvement in device reliability and electrical performances has been achieved.     

ALD of LaHfOx nano-laminates for high-κ gate dielectric applications

Electrical properties and thermal stability of LaHfO_x nano-laminate films deposited on Si substrates by atomic layer deposition (ALD) have been investigated for future high-κ gate dielectric applications. A novel La precursor, tris(N,N′-diisopropylformamidinato) lanthanum [La(ⁱPrfAMD)₃], was employed in conjunction with conventional tetrakis-(ethylmethyl)amido Hf (TEMA Hf) and water (H₂O). The capacitance-voltage curves of the metal oxide semiconductor capacitors (MOSCAPs) showed negligible hysteresis and frequency dispersion, indicating minimal deterioration of the interface and bulk properties. A systematic shift in the flat-band voltage (V_fb) was observed with respect to the change in structure of nano-laminate stacks as well as La₂O₃ to HfO₂ content in the films. The EOTs obtained were in the range of ∼1.23-1.5 nm with leakage current densities of ∼1.3 × 10⁻⁸ A/cm² to 1.3 × 10⁻⁵ A/cm² at V_fb − 1 V. In addition, the films with a higher content of La₂O₃ remained amorphous up to 950 °C indicating very good thermal stability, whereas the HfO₂ rich films crystallized at lower temperatures.     

Low-cost supercritical CO2/H2O2 treatment on ITO anodes of fluorescent organic light-emitting diodes

A simple and cost-effective approach is proposed as an alternative to conventional oxygen plasma treatment to modify surface property of Indium tin oxide (ITO) anode of a fluorescent organic light-emitting diode (OLED). This was achieved by treating the ITO anode in supercritical CO₂ (SCCO₂) fluids with hydrogen peroxide (H₂O₂). The SCCO₂/H₂O₂ treatment yielded an ITO work function of 5.35 eV after 15 min treatment at 85 °C and 4000 psi, which was significant higher than 4.8 eV of the as-cleaned ITO surface and was slightly less than 5.5 eV of the ITO surface treated by oxygen plasma. The highest work function achieved was 5.55 eV after 45 min SCCO₂/H₂O₂ treatment. The SCCO₂/H₂O₂ treatment can be used to tailor the ITO work function through changing the operation pressure of the treatment. In addition, the correlated dependence of OLED performance on the ITO anodes with and without the treatments was investigated. The maximum power efficiency of 1.94 lm/W was obtained at 17.3 mA/cm² for the device with 15 min SCCO₂/H₂O₂ treatment at 4000 psi. This power efficiency was 19.3% and 33.8% higher than those of the oxygen plasma treatment and as-clean, respectively. The improvement in device efficiency by the SCCO₂/H₂O₂ treatments can be attributed to enhanced hole injection and balance in charge carriers due to increased work function and surface energy of the ITO anodes.     

Tuning the dielectric properties of hafnium silicate films

The influence of Si concentration in hafnium silicate dielectrics on thermal stability and dielectric permittivity was analyzed. A phase diagram was developed using GIXRD and FTIR measurement. The stabilization of the “higher-k” cubic/tetragonal phase for annealing temperatures up to 1000 °C with a steady increase in capacitance was demonstrated for Hf_0.94Si_0.06O₂ films. It was also shown that the stabilization of nano-crystalline Hf_0.80Si_0.20O₂ films can be realized for annealing temperatures up to 900 °C. The influence of TiN electrodes on the dielectric constant and the leakage current characteristic was also investigated. A permittivity increase for annealing temperatures up to 1000 °C without degradation of leakage current was shown.     

InGaAs and Ge MOSFETs with high κ dielectrics

InGaAs and Ge MOSFETs with high κ’s are now the leading candidates for technology beyond the 15 nm node CMOS. The UHV-Al₂O₃/Ga₂O₃(Gd₂O₃) [GGO]/InGaAs has low electrical leakage current densities, C-V characteristics with low interfacial densities of states (D_it’s) and small frequency dispersion in both n- and p-MOSCAPs, thermal stability at temperatures higher than >850 °C, a CET of 2.1 nm (a CET of 0.6 nm in GGO), and a well tuning of threshold voltage V_th with metal work function. Device performances in drain currents of >1 mA/μm, transconductances of >710 μS/μm, and peak mobility of 1600 cm²/V s at 1 μm gate-length were demonstrated in the self-aligned, inversion-channel high In-content InGaAs n-MOSFETs using UHV-Al₂O₃/GGO gate dielectrics and ALD-Al₂O₃. Direct deposition of GGO on Ge without an interfacial passivation layer has given excellent electrical performances and thermodynamic stability. Self-aligned Ge p-MOSFETs have shown a high drain current of 800 μA/μm and peak transconductance of 420 μS/μm at 1 μm gate-length.     

A New Type of Efficient CO2 Adsorbent with Improved Thermal Stability: Self‐Assembled Nanohybrids with Optimized Microporosity and Gas Adsorption Functions

A new type of efficient CO₂ absorbent with improved thermal stability is synthesized via self‐assembly between 2D inorganic nanosheets and two kinds of 0D inorganic nanoclusters. In these self‐assembled nanohybrids, the nanoclusters of CdO and Cr₂O₃ are commonly interstratified with layered titanate nanosheets, leading to the formation of highly microporous pillared structure with increased basicity of pore wall. The co‐pillaring of basic CdO with Cr₂O₃ is fairly effective at increasing a proportion of micropores and reactivity for CO₂ molecules and at improving the thermal stability of the resulting porous structure. Of prime importance is that the present inorganic‐pillared nanohybrids show highly efficient CO₂ adsorption capacity, which is much superior to those of many other absorbents and compatible to those of CO₂ adsorbing metal?organic framework (MOF) compounds. Taking into account an excellent thermal stability of the present nanohybrids, these materials are very promising CO₂ adsorbents usable at elevated temperature. This is the first example of efficient CO₂ adsorbent from pillared materials. The co‐pillaring of basic metal oxide nanoclusters employed in this study can provide a very powerful way of developing thermally stable CO₂ adsorbents from many known pillared systems.     

An easily made thienoacene comprising seven fused rings for ambient-stable organic thin film transistors

A novel easily made thienoacene-based organic semiconductor, i.e., dinaphtho[3,4-d:3′,4′-d′]benzo[1,2-b:4,5-b′]dithiophene (Ph5T2), was synthesized in high yield, and its thermal stability, electrochemical properties, thin-film morphology and field-effect mobility were investigated. Ph5T2 exhibit excellent thermal stability with a decomposition temperature (T_d) of 427 °C. Thin-film X-ray diffraction (XRD) and atomic force microscopy (AFM) characterizations indicate that Ph5T2 can form highly ordered films with large domain size on the para-sexiphenyl (6P)-modified substrates. Organic thin-film transistors (OTFTs) with top-contact geometry based on Ph5T2 exhibit mobilities up to 1.2 cm² V⁻¹ s⁻¹ in ambient. The devices are highly stable and exhibit almost no performance degradation during 3 months storage under ambient conditions with relative humidity up to 80%.     

Investigation of interfacial reaction between Au-Sn solder and Kovar for hermetic sealing application

The microstructural evolution and interfacial reactions of Au/Sn/Au/Au/Ni/Kovar joint were investigated during aging at 180 and 250 °C for up to 1000 h. The Au/Sn combination formed a rapid diffusion system. Even in non-annealed joint, three phases such as AuSn, AuSn₂ and AuSn₄ were formed. After initial aging at 180 °C, the AuSn, AuSn₂, AuSn₄, Au and Sn phases, which were formed after plating, were fully transformed into ζ-phase and δ-phase, and (Ni, Au)₃Sn₂ intermetallic compound (IMC) layer was observed between the ζ-phase and Kovar. As a whole, the microstructure of the joint was stable during aging at 180 °C. On the other hand, the solid-state interfacial reaction was much faster at 250 °C than at 180 °C. During aging at 250 °C, the Ni layer on the Kovar reacted primarily with the δ-phase in the solder, resulting in the formation and growth of the (Au, Ni)Sn IMC layer at the interface. After aging for 48 h, the Fe-Co-Ni-Au-Sn phase was formed underneath the (Au, Ni)Sn IMC layer. Furthermore, cracks were observed inside the interfacial layers after complete consumption of the Ni layer. The study results clearly demonstrate the need for either a thicker Ni layer or an alternative surface finish on Ni, in order to ensure the high temperature reliability of the Au/Sn/Au/Au/Ni/Kovar joint above 250 °C.     

Planar micro-direct methanol fuel cell prototyped by rapid powder blasting

We present a planar micro-direct methanol fuel cell (μ-DMFC) fabricated by rapid prototyping-powder blasting technology. Using an elastomeric mask, we pattern two parallel microfluidic channels in glass. The anode and cathode of the fuel cell are formed by wet spraying Pt-Ru/C and Pt/C catalysts, respectively, onto Au electrodes that are evaporated in the microchannels. Simply clamping a Nafion 117 proton exchange membrane (PEM) using a glass substrate covered with PDMS membrane onto the microchannels completes the fuel cell fabrication. Our μ-DMFC generates a voltage of 0.45 V and can deliver a power up to 0.5 mW/cm² by using 1 M CH₃OH in 0.5 M H₂SO₄ solution as fuel in the anodic channel, and 0.01 M H₂O₂ in 0.5 M H₂SO₄ as oxidant solution in the cathodic channel.     

Dielectric properties in Au/SnO2/n-Si (MOS) structures irradiated under Co-γ rays

The metal-oxide-semiconductor (MOS) structures with insulator layer thickness range of 55-430 Å were stressed with a bias of 0 V during ⁶⁰Co-γ ray source irradiation with the dose rate of 2.12 kGy/h and the total dose range was 0-5×10⁵ Gy. The real part of dielectric constant ε′, dielectric loss ε″, dielectric loss tangent tanδ and the dc conductivity σ_dc were determined from against frequency, applied voltage, dose rate and thickness of insulator layer at room temperature for Au/SnO₂/n-Si (MOS) structures from C-V capacitance and G-V conductance measurements in depletion and weak inversion before and after irradiation. The dielectric properties of MOS structures have been found to be strongly influenced by the presence of dominant radiation-induced defects. The frequency, applied voltage, dose rate and thickness dependence of ε′, ε″, tanδ and σ_dc are studied in the frequency (500 Hz-10 MHz), applied voltage (−10 to 10 V), dose rate (0-500 kGy) and thickness of insulator layer (55-430 Å) range, respectively. In general, dielectric constant ε′, dielectric loss ε″ and dielectric loss tangent are found to decrease with increasing the frequency while σ_dc is increased. Experimental results shows that the interfacial polarization can be more easily occurred at the lower frequency and/or with the number of density of interface states between Si/SnO₂ interfaces, consequently, contribute to the improvement of dielectric properties of Au/SnO₂/n-Si (MOS) structures.     

OLED compatible water-based nanolaminate encapsulation systems using ozone based starting layer

Highly efficient nanolaminate diffusion barriers made of TiO₂/Al₂O₃ multilayers using low temperature atomic layer deposition optimized for organic light emitting diodes are presented. Water vapour transmission rates (WVTR) show values of the order of 10⁻³ g/m²/d at 38 °C, 90% RH on planarized PEN webs (pPEN) when ozone is used as the oxidizing precursor for Al₂O₃ deposition. OLED encapsulated with such diffusion barriers display few dark spots observed over 2000 h after deposition and for aging under ambient conditions. Diffusion barriers deposited using water as the oxidizing precursor for Al₂O₃ result in at least 10 times lower WVTR on pPEN webs (10⁻⁴ g/m²/d). However, these water based diffusion barriers are incompatible with OLEDs such that the latter show extensive black spot formation (areas of no visible luminescence) immediately after deposition. Finally through the growth of these initial black spots, more than 40% loss in initial luminescence occurs after merely 900 h of operation. In this report, we introduce a new methodology for OLED encapsulation using a two step process where 10 nm thick ozone Al₂O₃ based nanolaminate diffusion barrier is followed by a 90 nm thick water Al₂O₃ based diffusion barrier (keeping TiO₂ precursors always the same). With this novel diffusion barrier stack, no visible black spot growth is observed over 2000 continuous operation hours under ambient conditions. Simultaneously, high OLED luminescence representing 90% of the initial luminescence value, which is measured at t = 0 is maintained after 2000 h of operation. Low WVTR values in the 10⁻⁴ g/m²/d range on pPEN webs are consistently measured in these essentially water based barrier layers with only 10 nm thick starting ozone Al₂O₃ based nanolaminate diffusion barriers. The results reported here have implications on developing methodologies for ultra high performance, OLED compatible diffusion barriers by ALD.     

The intramolecular π–π stacking interaction does not always work for improving the stabilities of light-emitting electrochemical cells

Recently, the stabilities of light-emitting electrochemical cells (LECs) based on cationic iridium(III) complexes with controlled intramolecular π–π stacking interactions by adopting pendant phenyl rings have been dramatically enhanced compared with those of the complexes without π–π stacking interactions within the molecule. Herein, a novel cationic iridium complex [Ir(ppy)₂(pyphmi)]PF₆[ppy = 2-phenylpyridine, pyphmi = 1-pyridyl-3-phenylimidazolin-2-ylidene-C,C²′] which exhibits intramolecular π-stacking interaction has been prepared and its X-ray crystal structure has been investigated. Unexpectedly, however, the corresponding LECs based on [Ir(ppy)₂(pyphmi)]PF₆ do not show significantly enhanced stabilities compared to the LECs based on [Ir(ppy)₂(pymi)]PF₆ [pymi = 1-pyridyl-3-methylimidazolin-2-ylidene-C,C²′] without pendant phenyl rings within the molecule. This phenomenon is attributed to the very long centroid–centroid distance between the π-stacked phenyl rings, which results from the larger tension of substituted five-membered ring moiety (imidazolin-2-ylidene). In addition, irreversible oxidation and reduction processes would also decrease the electrochemical stability of [Ir(ppy)₂(pyphmi)]PF₆. Thus, intramolecular π–π stacking interaction using pendant phenyl rings is not always effective to improve the stability of LECs.