铁电薄膜可调带通滤波器

铁电薄膜的介电常数随外加电场强度的增加而减小.依据铁电薄膜的这一特性,提出了一种新颖的基于共面传输线结构的铁电薄膜可调带通滤波器.为了减小传输损耗,滤波器的导体部分由超导薄膜构成.滤波器的输入输出采用抽头线的方式分别与谐振器相接,外加电压通过输入输出端口直接施加到共面谐振器缝隙处的铁电薄膜上,用以改变铁电薄膜的介电常数,从而改变谐振器的谐振频率,实现带通滤波器通带频率的移动.这种新型可调带通滤波器具有结构紧凑、尺寸小及施加外加偏压容易等优点.仿真结果表明:铁电薄膜的介电常数在外加偏压下从250减小到150时,带通滤波器的传输特性曲线的形状基本保持不变,通带的中心频率从10.283GHz增加到10.518GHz,其3dB带宽保持在0.150GHz左右,反射损耗始终小于-17dB.     

铁电体电源起爆金属桥箔的数值计算分析

 为探讨铁电体电源对金属桥箔的起爆作用,对冲击波作用下PZT95/5铁电体对铜桥箔的放电过程进行了数值计算。通过引入金属桥箔电阻非线性变化的FIRESET模型,考虑回路电感及回路电阻,计算了负载为铜桥箔时的铁电体的电响应。讨论了铁电体并联数量、回路电感对桥箔爆炸特性的影响。计算结果表明：当并联排列的铁电体电极面积达到0.006 m²以上时,在桥箔上可产生高于100 GA/m²的电流密度,能够有效起爆桥箔。而回路中存在适当的电感将有利于铁电体电源起爆桥箔。计算方法和结果能够为起爆金属桥箔的铁电体电源设计提供理论根据。     

Study of the effect of manganese impurities on dielectric characteristics of BSTO films

Capacitance voltage and current voltage characteristics of BSTO ferroelectric films containing a manganese dioxide impurity (～1.5–2 mol%) are compared to those of impurity-free samples. It is shown that in Mn-doped samples tan δ drops to 10^?3, and the dependence of tan δ on the applied voltage changes as well. IVCs of these samples are strictly ohmic and do not show a nonlinearity at high voltages. A mechanism is proposed of the effect of Mn on the charge state of the defects comprising oxygen vacancies in BSTO films.     

铌镁酸铅-钛酸铅铁电阴极电子发射特性

研究了铌镁酸铅-钛酸铅铁电材料的铁电、介电性能对阴极发射阈值电压的影响, 以及铁电阴极发射电流与激励脉冲电压和抽取电压之间的关系, 并分析了其发射机理. 结果表明, 室温介电常数高、极化强度变化量大的弛豫铁电体0.9Pb(Mg_1/3Nb_2/3)O₃-0.1PbTiO₃具有较小的发射阈值电压; 铁电阴极电子发射与快极化反转和等离子体的形成有关; 由极化反转所致电子发射的自发射电流随激励脉冲电压的增大呈幂律增长关系, 其发射电流开始于激励脉冲电压的下降沿; 在抽取电压较大时, 发射电流随抽取电压的增大呈线性增长关系, 说明大电流主要取决于抽取电压; 其发射电流开始于激励脉冲电压的上升沿, 与“三介点”处的场增强效应和等离子体的形成有关; 当抽取电压为2500 V 时, 得到的发射电流幅值为210 A, 相应的电流密度为447 A/cm².     

铁电体电源中介质电阻特性及对输出电荷的影响

爆炸驱动铁电体脉冲电源利用铁电陶瓷在冲击压力作用下去极化释放电荷而产生电流,可以作为脉冲功率源的初始电源,也可直接驱动高阻抗负载产生脉冲高电压。通常情况下,铁电陶瓷可以看作理想的绝缘体,但在数GPa冲击波压力作用下,铁电陶瓷电阻率可能会明显下降并形成漏电导,使部分去极化释放电荷在铁电陶瓷内部流失,导致铁电陶瓷剩余极化电荷输出效率下降。以PZT95/5铁电陶瓷作为初始储能介质,以爆炸冲击波加载PZT95/5铁电陶瓷释放电荷对脉冲电容器充电,充电结束后电容器电压维持期间检测到明显的反向电流,根据铁电陶瓷输出电流和工作电压,得到冲击波作用过程中铁电陶瓷的瞬态电阻率曲线,并分析了电阻率下降对输出电荷的影响。进一步研究表明,冲击压力在铁电陶瓷边侧产生的稀疏波是引起电荷输出效率降低的主要因素,而铁电陶瓷电阻率下降对电荷输出效率的影响很小。     

掺镧锆锡钛酸铅陶瓷极化强度变化量对电子发射电流强度的影响

铁电阴极因其优异的电子发射性能在高功率微波管的电子束源、平板显示技术以及宇航推进器等领域 有着广阔应用前景而日益受到人们的重视.大量研究表明,铁电阴极电子发射性能受阴极材料性能的影响. 在激励电场作用下,铁电阴极材料会产生表面非屏蔽电荷而引起极化强度的变化, 这表明铁电阴极电子发射性能可能与阴极材料的极化强度变化量存在着某种关系. 为研究阴极材料极化强度变化量对铁电阴极电子发射性能的影响,以掺镧锆锡钛酸铅铁电和反铁电陶瓷样品 作为阴极材料,通过正半周电滞回线测试得到阴极材料在不同电场强度下的极化强度变化量, 测量得到电子发射电流强度随激励电场的变化曲线,并分析了电子发射电流强度与极化强度变化量的关系. 结果表明,两种样品电子发射电流强度与极化强度变化量正相关.     

Interrupting capacity of vacuum interrupters depending on thefrequency of current

Results of arc reignition voltages during current interruption of frequencies from 5.9 to 60 kHz by a short vacuum gap are presented. Measured arc reignition voltages depend on current amplitude and frequency, the values of preliminary arc current at the moment of switching on the HF current, and the discharge mode in the preceding current semiwave. Threshold amplitudes of the first semiwave of currents l_m1l and I_m1h as a function of frequency are determined. I_m1l and I_m1h divide current into three ranges to which different kinds of arc reignition voltage distribution correspond. Particularly large dispersion of reignition voltages takes place in the current range from I_m1l to I_m1h. The threshold current I_m1h is inversely proportional to frequency in the range from about 10 to 60 kHz, which is in agreement with the elaborated mathematical model     

Ferroelectric effect and equivalent polarization charge model of PbZr_(0.2)Ti_(0.8)O_3 on AlGaN/GaN MIS-HEMT

PbZr_(0.2)Ti_(0.8)O_3(PZT) gate insulator with the thickness of 30 nm is grown by pulsed laser deposition(PLD) in AlGa N/Ga N metal–insulator–semiconductor high electron mobility transistors(MIS-HEMTs). The ferroelectric effect of PZT Al Ga N/Ga N MIS-HEMT is demonstrated. The polarization charge in PZT varies with different gate voltages. The equivalent polarization charge model(EPCM) is proposed for calculating the polarization charge and the concentration of two-dimensional electron gas(2 DEG). The threshold voltage(Vth) and output current density(IDS) can also be obtained by the EPCM. The theoretical values are in good agreement with the experimental results and the model can provide a guide for the design of the PZT MIS-HEMT. The polarization charges of PZT can be modulated by different gate-voltage stresses and the Vthhas a regulation range of 4.0 V. The polarization charge changes after the stress of gate voltage for several seconds. When the gate voltage is stable or changes at high frequency, the output characteristics and the current collapse of the device remain stable.     

Development of a ferroelectric cathode diode

As a promising kind of high current cold cathode,the Ferroelectric Cathode(FEC)has several significant advantages,such as a controllable trigger time,lower vacuum requirement and large emitting area fabricability.The emitting current density of the FEC fabricated at Tsinghua University was more than200 A/cm2.In order to make the ferroelectric cathode into practical applications,a high current density diode using a ferroelectric cathode was designed,based on the PIC simulation.The performance of the FEC diode was investigated experimentally.When the applied diode voltage was 60 kV,a current density of more than250 A/cm2 was obtained,and the current density distribution was also measured.     

Au/PZT/BIT/p-Si异质结的制备与性能研究

采用脉冲激光沉积(PLD)工艺,制备了以Bi₄Ti₃O₁₂(BIT)为过渡阻挡层的Au/PZT/BIT/p-Si异质结.研究了BIT铁电层对Pb(Zr_0.52Ti_0.48)O₃(PZT)薄膜晶相结构、铁电及介电性能的影响,对Au/PZT/BIT/p-Si异质结的导电机制进行了讨论.氧气氛530℃淀积的PZT为多晶铁电薄膜,与直接淀积在Si基片上相比,加入BIT铁电层后PZT铁 关键词： 铁电薄膜 异质结构 脉冲激光沉积(PLD)     

Abnormal current-voltage characteristics and metal-insulator transition of amorphous carbon film/silicon heterojunction

The amorphous carbon film/n-Si (a-C/n-Si) heterojunctions have been fabricated by direct current magnetron sputtering at room temperature, and their current-voltage characteristics have been investigated. The results show that these junctions have good rectifying properties in the temperature range 80-300 K. The interesting result is that the current-voltage curve changes dramatically with increasing applied voltage and temperature. For the forward bias voltages, the junction shows Ohmic mechanism characteristic in the temperature range 240-300 K. However, the conduction mechanism changes from Ohmic for the low bias voltages to space charge limited current for the high bias voltages in the temperature range 80-240 K. While for the reverse bias voltages, it changes from Schottky emission to breakdown with increasing voltage. Another important phenomenon is that the temperature dependence of the junction resistance shows a metal-insulator transition, whose transition temperature can be controlled by the bias voltage.     

Piezoelectric non-linearity in PbSc0.5Ta0.5O3 thin films

Epitaxial (001)-oriented PbSc_0.5Ta_0.5O₃ (PST) thin films were deposited by pulsed laser deposition. Local piezoelectric investigations performed by piezoelectric force microscopy show a dual slope for the piezoelectric coefficient. A piezoelectric coefficient of 3 pm/V was observed at voltages up to 0.8 V. However, at voltages above 0.8 V, there is a steep increase in piezoelectric coefficient mounting to 23.2 pm/V. This nonlinear piezoelectric response was observed to be irreversible in nature. In order to better understand this nonlinear behavior, voltage dependent dielectric constant measurements were performed. These confirmed that the piezoelectric non-linearity is indeed a manifestation of a dielectric non-linearity. In contrast to classical ferroelectric systems, the observed dielectric non-linearity in this relaxor material cannot be explained by the Rayleigh model. Thus the dielectric non-linearity in the PST films is tentatively explained as a manifestation of a percolation of the polar nano regions.     

AC modulation of the recombination electroluminescence in anthracene single crystal

The recombination electroluminescence (REL) in an anthracene single crystal has been modulated by ac voltage at different dc biasing voltages. The frequency and ac voltage dependences observed are interpreted in terms of the presented model of sinusoidal current wave. The dc-voltage-induced changes in the modulation are explained by the voltage variation of the triplet exciton lifetime and wavelength of the current wave based on concomitant evolution of the triplet-to-singlet exciton concentration ratio responsible for the contribution of delayed and prompt components of the REL.     

铁电阴极前电极表面等离子体横向扩散速度估算

分析了激励脉冲电压作用下铁电阴极电容的变化,即等离子体沿着铁电阴极前电极表面扩散而引起电容变化;建立了激励脉冲电压作用下铁电阴极等效电容模型并推导铁电阴极前电极表面等离子横向扩散速度表达式。采用传统固相烧结工艺制备的掺镧锆锡钛酸铅反铁电陶瓷作为阴极材料,通过测量激励脉冲电压作用下铁电阴极两端的电压及充放电电流,计算得到掺镧锆锡钛酸铅陶瓷表面等离子体横向扩散速度为1.89×106 cm/s。     

Experimental observation of voltage amplification using negative capacitance for sub-60 mV/decade CMOS devices

In this study, an experimental study of negative capacitance is performed in order to overcome the physical limit of subthreshold slope (SS), SS ≥ 60 mV/decade at 300 K, which is originated from (i) using the thermionic emission process in complementary metal-oxide-semiconductor (CMOS) technology and (ii) non-scalability of the thermal voltage k_BT/q (i.e., in order to realize SS lower than 60 mV/decade at 300 K). To make the surface potential higher than the gate voltage, a step-up voltage amplifier is included in the CMOS gate stack using a ferroelectric capacitor implemented with ferroelectric material. The measured SS in long-channel CMOS transistors is 13 mV per decade at 300 K. A simple connection of the ferroelectric capacitor to a complementary metal oxide semiconductor (CMOS) gate electrode would provide a new evolutionary pathway for future CMOS scaling.     

强电流铁电阴极电性能参数与发射结果的关系研究

 在实验结果的基础上,从理论上阐述了材料的电滞回线、介电常数、压电常数等性能对电流发射性能的明显影响,并通过材料的掺杂改性提高材料的性能参数,从而达到了提高发射电流密度的目的。     

Pulsed Hollow Cathode Discharge with Nanosecond Risetime

This paper reports the operation of a cylindrical hollow cathode discharge with current risetimes of a few nanoseconds at current densities at the entrance of the cathode in the range of 50-560A · cm-2 and at voltages of 280-850 V. Time-dependent measurements of the impedance of the discharge are presented. They allow for the evaluation of discharge quantities such as risetime, delay time, discharge voltage, and current, depending on the operation parameters as applied voltage, pressure, and preionization. The power density in the active region of the hollow cathode exceeded 200 kW · cm-3.     

High-Power Opening-Closing Switches Using Grid-Controlled Plasmas

Two switches are described with the capability of rapidly interrupting high-power circuits: a vacuum triode with a large-area plasma cathode, and a grid-controlled plasma conduction switch. Theoretical models for the vacuum triode imply that it could control voltages in the range ?100 kV at current density ?2 × 104 A/m2. The vacuum switch has the advantage of rapid switching at the expense of reduced efficiency because of its significant anode-cathode voltage drop. In contrast, the plasma switch has almost zero voltage in the conducting state. The theoretical models presented indicate that the plasma switch could conduct current densities in the range 10 × 104 A/m2 with open-circuit voltage ? 100 kV. Although the closing time is long (~1 ?s), the predicted opening time is short (~20 ns). Initial experiments demonstrating the principle of operation of the plasma switch are reported.     

Limiting current oxygen sensors for the percentage to ppm range

Oxygen sensors based on the limiting current principle were investigated by employing TZP (tetragonal zirconia polycrystals) as solid electrolyte. Current-voltage curves of the sensors indicate that the operation temperature may be as low as 330 °C in air and at lower oxygen concentration. A linear relationship is observed from 1 to 20 % oxygen in argon gas. The temperature dependence of the sensor's output current is presented which limits the operating temperature range under the condition of a constant applied voltage. The critical parameters of limiting current oxygen sensors which may work in the ppm range are discussed. A linear current signal is obtained at optimized temperatures and applied voltages. The sensor shows many potential applications in fields of controlling inert process gases and leak detection. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, 13–19 Sept. 1997.     

Electron tunneling through superconducting A1/monolayer/Pb junctions

The current-voltage characteristic of Al/adsorbed monolayer/Pb junctions was measured at 77, 4.2 and 1.8K at applied voltages from 1 to 3 mV. At 77K the current changes linearly with voltage whereas at 4.2 and 1.8 K the relationship becomes nonlinear. From the results at 1.8 K we obtain an approximate band gap for Pb equal to 2.6 meV. The observation of a nonlinear current-voltage characteristic at temperatures where Pb becomes superconducting is strong evidence that the observed current through the insulator is a tunneling current.