High-efficiency millimetre-wave silicon impatt oscillators

High-efficiency impatt devices and oscillators have been fabricated from epitaxially grown silicon for operation in the frequency range 40?140 GHz. These devices have produced world state-of-the-art efficiencies and demonstrated the expected relative frequency insensitivity of silicon. Single drift devices have given efficiencies of approximately 8%; and double drift device efficiencies as high as 13.5% at 50 GHz and 12% at 90 GHz. Initial measurements show that the sideband phase noise levels follow a constant deviation law.     

Optical injection locking of impatt oscillators

A method for locking impatt oscillators by illuminating the impatt diode with a low-power laser beam, amplitude modulated at microwave frequency, is described. A large-signal theory of impatt operation, including the effects of finite reverse saturation currents and their modulation by the laser beam, is presented and predicts locking ranges of several tens of MHz with laser powers of a few mW     

Reduction of FM noise in impatt oscillators by optical illumination

Experiments are described in which laser illumination of the active device has reduced the FM noise output by up to 5 dB for a GaAs impatt oscillator and 2 dB for a Si impatt oscillator. A qualitative explanation of the observed results is given, and the effect of laser amplitude noise on the maximum noise reduction obtainable is shown.     

Performance enhancement of ring oscillators and transimpedance amplifiers by package strain

The appropriate external stress can enhance a device and circuit performance. The 7.4% speed enhancement is achieved for the 250-nm node ring oscillator under uniaxial tensile strain for a mutually perpendicular layout of the NFET and the PFET. The speed enhancement is less than 1.5% for the conventional parallel layout of the NFET and the PFET. A 180-nm node transimpedance amplifier has a /spl sim/ 5% bandwidth enhancement using a biaxial tensile strain or a uniaxial tensile strain parallel to the NFET channel to tune the peaking frequency of active inductor in the circuit. The package strain can provide an extra useful parameter for the future digital and analog circuit design.     

Intermodulation distortion improvement by active compensation in impatt amplifiers

The letter discusses how the intermodulation distortion in impatt diode amplifiers can be improved significantly by active compensation. Theoretical evaluation based on a large-signal impatt diode model predicts considerable improvement in the intermodulation behaviour; in particular, the improvement in the third-order intercept point is found to be in excess of 12 dB.     

IMPATT oscillators with enhanced leakage current

The behavior of IMPATT oscillators with enhanced leakage current has been experimentally evaluated by irradiating operating diodes with transient ionizing radiation. Leakage current was induced in diffused junction GaAs and silicon X-band IMPATT diodes by irradiation with 100 nsec pulses of 10 MeV electrons. With increasing leakage current, the oscillator RF power decreases and the frequency of oscillation increases. A large signal circuit model of the IMPATT diode is developed which correlates well with experimental measurements.     

Wien bridge oscillators using current conveyors

Realization of oscillators with single resistor control based on the circuit techniques of the second generation current conveyors (CC II) utilizing the separability of the Wien RC one-ports that are generalized through appropriate insertion of two more resistors is considered. The relative frequency stability is shown to improve over the conventional op-amp Wien bridge versions.     

Leakage current mechanism in sub-micron polysilicon thin-filmtransistors

We have studied leakage current in sub-micron p-channel polysilicon thin-film-transistor. Our study revealed that thermionic emission is the dominant mechanism at low drain bias (-0.1 V) while thermionic field emission dominate at moderately high drain bias. At high drain bias (>-5.0 V), tunneling was observed to be the dominant leakage mechanism     

Novel MOS-C oscillators using the current feedback op-amp

Three new MOS-C oscillators using the current feedback op-amp are presented. The proposed oscillators have the advantage of independent control of the oscillation frequency and the condition of oscillation. Two of the proposed MOS-C oscillators provide two outputs in phase quadrature. The third proposed oscillator provides two outputs in the balanced form. PSpice simulation results for the proposed oscillators are given.     

Voltage controlled oscillators using complementary current mirror inverter

Complementary current mirror inverters have large bandwidth, small time delay but small gain whereas complementary inverters have high gain but large time delay. Ring oscillators have been realised using a combination of both types of inverter to achieve stable high frequency oscillation. Voltage controlled oscillators were obtained by tuning the frequency of oscillation with supply voltage.<>     

Multiphase sinusoidal oscillators using second generation current conveyors

A voltage-mode Multiphase Sinusoidal Oscillator realized using Second Generation Current Conveyors and only grounded passive elements is introduced in this paper. The proposed topology is suitable for realizing oscillators with both odd and even number of phases without modifying the core of the topology. Only non-inverting Current Conveyors are required for the construction of the oscillator's topology and this is a benefit from the discrete component implementation point of view. The behavior of the proposed topology has been evaluated, through experimental results, in the cases of three and six-phase oscillators.     

Mode competition,suppression, and efficiency enhancement in overmoded gyrotron oscillators

Gyrotron oscillators are of great interest as sources of high power mm wave radiation for electron cyclotron resonance heating and current drive in magnetic fusion research devices. Gyrotrons capable of efficiently generating cw power ? 1 megawatt will be required in future magnetic fusion studies. However, as gyrotron power approaches the megawatt level, a very large, overmoded cavity must be employed in order to keep ohmic power losses in the cavity at an acceptable level, and the problem of mode overpopulation becomes severe. Also, it becomes increasingly important to optimize gyrotron efficiency for a number of important reasons including minimizing the problem of collecting the electron beam energy. In the present paper, a detailed experimental and theoretical study of mode competition and mode locking in an overmoded gyrotron is presented. Efficiency enhancement (to 60%) and high peak power (430 kW) were achieved in the TE_2,4,1 mode using magnetostatic profiling in the cavity. With selective mode suppression, peak power of 475 kW was generated in the TE_0,4,1 mode.     

Leakage current characteristics of offset-gate-structure polycrystalline-Silicon MOSFET's

Leakage current characteristics of offset-gate-structure polycrystalline-silicon (poly-Si) MOSFET's are studied as a function of dopant concentration Noffin offset-gate regions. Leakage current markedly decreases from 1 × 10^-9to 2 × 10^-11A at VD= 10 V as Noffis varied from 1 × 10¹⁸to 1 × 10¹⁷cm^-3. A maximum ON/OFF current ratio of 10⁸is obtained at 1 × 10¹⁷cm^-3. Calculations based on a quasi-two-dimensional model indicate that the reduction of leakage current is attributable to a decrease of the maximum lateral electric field strength in the drain depletion region. An analysis of the leakage current characteristics in terms of carrier emission from grain-boundary traps implies that thermonic emission accompanied by thermally assisted tunneling could be the dominant mechanism in determining leakage current.     

Leakage current degradation in n-MOSFETs due to hot-electron stress

The field-induced drain-leakage current can become significant in NMOS devices with thin gate oxides. This leakage current component is found to be more prominent in devices with gate-drain overlap and can increase considerably with hot-electron stress. A method which shows how measuring the gate voltage needed to obtain a constant leakage value of 0.1 nA can yield useful information on the interface charge trap density is discussed     

Emission current enhancement of MIM cathodes by optimizing thetunneling insulator thickness

The relationship between the thickness of the anodized Al₂ O₃ tunneling insulator and the transfer ratio was investigated for metal-insulator-metal (MIM) cathodes to optimize the thickness in terms of a high transfer ratio and emission current. Combining ellipsometry, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM), we determined the accurate thickness of an anodized Al film less than 20 nm-thick. With the knowledge of accurate thickness, we found that the transfer ratio increases as the insulator thickness increases from 5.2 nm to 10.6 nm, but saturates at 13.3 nm and decreases slightly at 20.1 nm. Optimizing the thickness of the insulator to 13.3 nm raised the transfer ratio of 0.1% for our previous work (Kusunoki and Suzuki, IEEE Trans. Electron Devices, vol. 47, pp. 1667-1672, 2000) to 0.7%. A high emission current of 14 mA/cm² was thus obtained. The existence of an optimal thickness for the anodized Al₂O₃ insulator was also clarified from a theoretical simulation. This is the result of a trade-off, as thickness increases, between the decreasing probability of cut-off at the surface workfunction barrier of the Ir-Pt-Au top electrode and the increased scattering of hot electrons inside the Al ₂O₃ insulator and top electrode. The relationship is discussed on the basis of the absolute distribution of energy of the hot electrons, which we determined by simulating inelastic scattering driven by electron-optical phonon interaction in the Al₂O₃ insulator     

Simultaneous observations of current and voltage waveforms of Gunn oscillators

Simultaneous observations were made of current and voltage waveforms of Gunn oscillators mounted in a resistive circuit. From the results of the observations, the efficiency of resistively loaded Gunn oscillators is studied for applied voltages and load resistances, and some quantities for a high-field domain are also discussed for applied voltages.     

Leakage current modeling of series-connected thin film transistors

The leakage current of an arbitrary number of series-connected polysilicon Thin Film Transistors (TFTs) with a common gate is shown to be easily computed from the I-V characteristics of a single FET for the first time, both by an analytical model and by graphical techniques. Good agreement with experimental data is obtained for drain biases greater than /spl sim/1 V. The work is also applicable to single crystal Silicon-On-Insulator (SOI) TFTs.<>