Key Engineering Materials Vols. 645-646

Abstract: We have developed a combination of electro –deposition and spraying methods to prepare water-repellent tin oxide/ polytetrafluoroethylene(SnO2/PTFE) coating. The coating has a high water contact angle. The resulting porous and lowest surface energy hydrophobic groups (－CF3) has a water contact angle of 165° and a sliding angle of 7°, showing super-hydrophobic property. The coating with good adhesion on substrates and the long-term stability can be fabricated on various metal substrates.

Abstract: A silicon magnetic sensitivity transistor (SMST) with negative resistance oscillations phenomenon is presented in this paper, which is constituted by emitter (E), base (B) and collector (C). The SMST chip is fabricated on <100> orientation high resistivity C-type silicon cup by using MEMS technology. Experiment results show, when external magnetic field B=0 T, base injection current I_b is the scope of 1.5mA to 1.7mA and V_CE is greater than 4.0V, the collector current I_c appears negative resistance oscillation phenomenon, the oscillation frequency will increase with the increase of the V_CE. I_c changes with external magnetic field B, where V_CE and I_b are constant. With the condition of the I_b=1.5 mA and V_CE=9.0 V, the oscillation frequency of B=0 mT and B=-150 mT are 5.88 kHz and 7.60 kHz, respectively.

Abstract: Monodisperse CoFe₂O₄ and Co_0.4Zn_0.6Fe₂O₄ hollow nanospheres were synthesized in large scale by solvothermal method in ethylene glycol solution. The structure, shape and size of the samples were investigated by Fourier Transform infrared, X-ray powder diffraction and scanning electron microscopy. The results indicate that the products are spherical with an average diameter less than 200 nm. Magnetic studies revealed that the saturation magnetization of Co_0.4Zn_0.6Fe₂O₄ is 78.6 emu/g, higher than the CoFe₂O₄, which is 69 emu/g, while the coercivity of the Co_0.4Zn_0.6Fe₂O₄ is 184 Oe , obviously lower than that of CoFe₂O₄ which is 832 Oe. The electromagnetic parameters were measured at 2-18 GHz using HP8722ES vector network analyzer and then the microwave absorption properties were calculated through the transmission line theory. As to the Co_0.4Zn_0.6Fe₂O₄, the absorption bandwidth with reflection loss below-10 dB is up to 3GHz, from 10GHz to 13GHz with a thickness of 2 mm. A maximum reflection loss-45.6 dB was found at 12.9 GHz for the CoFe₂O₄ with a thickness of 1.8 mm. As a result, the as-prepared hollow nanospheres show good prospects of being applied in EM wave absorption materials.

Abstract: The split-drain magnetic field effect transistor (MAGFET) based on nanopolysilicon thin film transistor (TFT) is fabricated on <100> high resistivity silicon substrates by (complementary metal oxide semiconductor) CMOS technology in this paper. It contains source (S), drain1 (D₁), drain2 (D₂) and gate (G), and adopts nanopolysilicon thin films and nanopolysilicon/high resistivity silicon heterojunction interfaces as the magnetic field sensing layers. The influence of the channel size and shapes on the transistor, are studied to further improve its magnetic sensitivity. When the ratio of channel length and width (L/W) of MAGFET is 80 μm/160 μm, V_DS=5.0 V, the MAGFET with convex channel has higher magnetic sensitivity than the rectangle and concave, the absolute current magnetic sensitivity S_I and the absolute voltage magnetic sensitivity S_V of the proposed sensor reach the maximum values, and are 0.021 mA/T and 55 mV/T, respectively.

Abstract: In this paper, a large signal circuit model of graphene field effect transistor (GFET) is described accurately by Verilog-A language, which is suitable for radio frequency circuit design and can be applied in HSPICE and ADS directly. Then two typical radio frequency (RF) circuits, frequency multiplier and mixer, are based on this GFET circuit model. The proposed circuits’ performance are analyzed respectively in 10GHz, 15GHz and 20GHz, and GFET’s application foreground in radio frequency area is discussed.

Abstract: The YBCO powder was prepared by oxalic acid precipitation method and consequent annealing. The correlation between pH values of oxalic acid solution and the precipitation percentage of precursors were analysed based on thermodynamics analysis. The differential scanning calorimetryanalysis (DSC) was used to confirm the synthetic technological parameter. The phases of powder in each process were investigated by XRD. The microstructures of each powder were tested by SEM and TEM. The mean grain size was calculated by the scherrer’s equation. The test results indicated that the YBCO powder with high purity, less impurities, smaller particle, but severe agglomeration, was Y123 when annealing at 900°C. However, adding dispersants could effectively solve the severe agglomeration. The size of YBCO particles was nanosized and coincided with the calculation.

Abstract: The size dependence becomes more significant as the devices scale down from micro-to nanodimensions, which is generally attributed to surface effects due to the very high surface-to-bulk ratios in nanoscale structures. However, significant discrepancies between experimental measurements and computational studies indicate that there could be other influences besides surface effects, such as the influences of native oxide layer, fabrication-induced defects and boundary conditions. In this paper, our purpose is to investigate mainly the influence of fabrication-induced defects on the elasticity of [110] silicon nanowires (SiNWs) with different cross sections. We accomplish this by using the molecular dynamics (MD) simulation. Our MD results show that the H-passivated [110] SiNWs without surface defects is slightly elastically softer than bulk, which is in good agreement with other literature MD values. However, the effective Young’s modulus of SiNWs with surface defects can significantly decreases as the defects increase. This softening behavior of [110] SiNWs is severe, which indicates the importance of surface defects. It is noted that the influence of defects on the Young's Modulus of SiNWs strongly depended on the distribution and morphology of defects as well as the cross-sectional shapes of SiNWs. It is observed that the influence of defects on square SiNWs is significantly different from those of hexagonal and triangle SiNWs. Our work reveals that fabrication-induced surface defects could be one of the important origins of the reduced effective Young’s modulus experimentally observed in ultra-thin SiNWs. Therefore, the effect of defects on the characterization of the mechanical properties of nanowire must be carefully considered.

Abstract: Large-scale silver nanoparticles with fine dispersion and narrow size distribution were synthesized by reducing silver nitrate with sodium borohydride and sodium citrate and using poly (vinylpyrrolidone) as an adsorption agent in the ethanol solution. The sintering behavior and electrical properties of silver nanoparticles treated with and without glutaric acid were studied. Morphology studies showed that the treated silver nanoparticles obviously agglomerated and began to sinter at 200 °C and the sintering temperature is higher at least 50 degrees than that of the untreated silver nanoparticles The treated silver nanoparticles as fillers of electronically conductive adhesives (ECAs) is more advantageous to the increase of the conductivity. Otherwise, only in the conditions of the appropriate sintering temperature and loading of silver nanoparticles, the high conductivity of the ECAs was obtained. The effect of the treated silver nanoparticles on the electrical properties contributes to the surface activation and sintering behavior.Keywords: Silver nanoparticle, Sintering Behavior, Surface treatment, Electrical property

Abstract: Polyimide is often used as a sacrificial layer material to make floating structure. Polyimide is also divided into photosensitive and non-photosensitive type; photosensitive polyimide currently has more negative photoresist and poor performance in many ways. Compared with photosensitive polyimide, the non-photosensitive type has low stress, stable performance and other advantages, so non-photosensitive polyimide has been chosen as a sacrificial layer material. To achieve the graphical function and release sacrificial layer, A deeply research was made in this dissertation makes on wet etching and dry etching. By controlling the wet etching process of prebake condition, exposure and developing time, and oxygen dry etching process of etching power, bias voltage and other key process parameters, a good sacrificial layer graph and etching effect have been got. Finally, it can be concluded that when the prebake conditions for 105°C, 8min and times of exposure and developing were 11s and 29s, the non-photosensitive polyimide wet etching effect is the best; when the etching power is 1000w, an oxygen flux rate is 50sccm, the reaction pressure is 30mTorr, the bias voltage is 140v, oxygen dry etching has a good effect.

Abstract: Pt/HfO_x/Pt resistive switching devices with symmetric electrodes were fabricated. Bipolar resistive switching (RS) behaviors and unipolar behaviors were then observed under a positive/negative bias applied to the top electrode (TE). A comparison and analysis of bipolar/unipolar RS behaviors under different voltage polarities was then performed.The results demonstrated that bipolar RS was achieved via a drift of anion (O^2-) under the electric field resulting in the rupture and recovery of filaments at the interface. When the filaments dissolved and formed at the interface near BE, the performance of the bipolar RS devices was better. However, for unipolar RS devices, when filaments dissolved and formed at the interface near TE, the performance was even better. These results indicated that a drift of O^2- caused by electric field and a diffusion of O^2- induced by Joule heat were the main reasons for unipolar RS. The different characteristics of the bipolar and unipolar devices can be attributed to the existence of a different number of defects at the active interface of the devices. This was where the rupture and recovery of filaments occurred. The results also indicate that the active interface is more important than other interfaces for RRAM performance.