Discharge characteristic of very high frequency capacitively coupled argon plasma

The discharge characteristics of capacitively coupled argon plasmas driven by very high frequency discharge are studied.The mean electron temperature and electron density are calculated by using the Ar spectral lines at different values of power(20 W-70 W)and four different frequencies(13.56 MHz,40.68 MHz,94.92 MHz,and 100 MHz).The mean electron temperature decreases with the increase of power at a fixed frequency.The mean electron temperature varies non-linearly with frequency increasing at constant power.At 40.68 MHz,the mean electron temperature is the largest.The electron density increases with the increase of power at a fixed frequency.In the cases of driving frequencies of 94.92 MHz and 100 MHz,the obtained electron temperatures are almost the same,so are the electron densities.Particle-in-cell/Monte-Carlo collision(PIC/MCC)method developed within the Vsim 8.0 simulation package is used to simulate the electron density,the potential distribution,and the electron energy probability function(EEPF)under the experimental condition.The sheath width increases with the power increasing.The EEPF of 13.56 MHz and 40.68 MHz are both bi-Maxwellian with a large population of low-energy electrons.The EEPF of 94.92 MHz and 100 MHz are almost the same and both are nearly Maxwellian.

A Novel Flexible Antenna at Very High Frequency Band for On-Body Applications

This paper proposes a novel flexible antenna design operating at very high frequency(VHF)band for on-body applications such as human body communication(HBC).The antenna consists of back-to-back E-shaped fractal and complimentary structures designed over a thin flex-ible substrate.The overall design working on the principle of fractal geometries and capacitive coupling is highly beneficial to achieve better antenna characteristics even at low frequencies around 35 MHz-45 MHz that are being used for HBC application.The proposed antenna obtained a large bandwidth of around 10.0 MHz in air and a bandwidth of around 8.0 MHz during on-body opera-tion.The antenna has been tested in three different scenarios viz.air,on-body single antenna and on-body communication using two antennas.The insertion loss is reduced to a minimum in all three scenarios,which is quite beneficial for better signal transmission.The size miniaturization with high flexibility in such low frequencies has also been achieved in the paper that makes the proposed design suitable for human body communication applications.

Target height and multipath attenuation joint estimation with complex scenarios for very high frequency radar

Low-angle estimation for very high frequency(VHF)radar is a difficult problem due to the multipath effect in the radar field,especially in complex scenarios where the reflection condition is unknown.To deal with this problem,we propose an algorithm of target height and multipath attenuation joint estimation.The amplitude of the surface reflection coefficient is estimated by the characteristic of the data itself,and it is assumed that there is no reflected signal when the amplitude is very small.The phase of the surface reflection coefficient and the phase difference between the direct and reflected signals are searched as the same part,and this represents the multipath phase attenuation.The Cramer-Rao bound of the proposed algorithm is also derived.Finally,computer simulations and real data processing results show that the proposed algorithm has good estimation performance under complex scenarios and works well with only one snapshot.

Fabrication of 3D air-core MEMS inductors for very-highfrequency power conversions

We report a fabrication technology for 3D air-core inductors for small footprint and very-high-frequency power conversions.Our process is scalable and highly generic for fabricating inductors with a wide range of geometries and core shapes.We demonstrate spiral,solenoid,and toroidal inductors,a toroidal transformer and inductor with advanced geometries that cannot be produced by wire winding technology.The inductors are embedded in a silicon substrate and consist of through-silicon vias and suspended windings.The inductors fabricated with 20 and 25 turns and 280-350μm heights on 4-16 mm2 footprints have an inductance from 34.2 to 44.6 nH and a quality factor from 10 to 13 at frequencies ranging from 30 to 72 MHz.The air-core inductors show threefold lower parasitic capacitance and up to a 140% higher-quality factor and a 230% higher-operation frequency than silicon-core inductors.A 33 MHz boost converter mounted with an air-core toroidal inductor achieves an efficiency of 68.2%,which is better than converters mounted with a Si-core inductor(64.1%).Our inductors show good thermal cycling stability,and they are mechanically stable after vibration and 2-m-drop tests.

Influence of total gas flow rate on microcrystalline silicon films prepared by VHF-PECVD

Hydrogenated microcrystalline silicon （μc-Si：H） films are fabricated by very high frequency plasma enhanced chemical vapour deposition （VHF-PECVD） at a silane concentration of 7% and a varying total gas flow rate （H2＋SiH4）. Relations between the total gas flow rate and the electrical and structural properties as well as deposition rate of the films are studied. The results indicate that with the total gas flow rate increasing the photosensitivity and deposition rate increase, but the crystalline volume fraction （Xc） and dark conductivity decrease. And the intensity of （220） peak first increases then decreases with the increase of the total gas flow rate. The cause for the changes in the structure and deposition rate of the films with the total gas flow rate is investigated using optical emission spectroscopy （OES）.

SUBSTRATE EFFECT ON HYDROGENATED MICROCRYSTALLINE SILICON FILMS DEPOSITED WITH VHF-PECVD TECHNIQUE

Raman spectra and scanning electron microscope （SEM） techniques were used to determine the structural properties of microcrb＇stalline silicon （μc-Si：H） films deposited on different substrates with the very high frequency plasma-enhanced chemical vapor deposition （VHF-PECVD） technique. Using the Raman spectra, the values of crystalline volume fraction Xc and average grain size d are 86%, 12.3nm; 65%, 5.45nm; and 38%, 4.05nm, for single crystalline silicon wafer, coming 7059 glass, and general optical glass substrates, respectively. The SEM images further demonstrate the substrate effect on the film surface roughness. For the single crystalline silicon wafer and Coming 7059 glass, the surfaces of the μc-Si：H films are fairly smooth because of the homogenous growth or h＇ttle lattice mismatch. But for general optical glass, the surface of the μ-Si： H film is very rough, thus the growing surface roughness affects the crystallization process and determines the average grain size of the deposited material. Moreover, with the measurements of thickness, photo and dark conductivity, photosensitivity and activation energy, the substrate effect on the deposition rate, optical and electrical properties of the μc-Si：H thin films have also been investigated. On the basis of the above results, it can be concluded that the substrates affect the initial growing layers acting as a seed for the formation of a crystalline-like material and then the deposition rates, optical and electrical properties are also strongly influenced, hence, deposition parameter optimization is the key method that can be used to obtain a good initial growing layer, to realize the deposition of μc-Si：H films with device-grade quality on cheap substrates such as general glass.

A common-gate bootstrapped CMOS rectifier for VHF isolated DC-DC converter

A common-gate bootstrapped CMOS rectifier dedicated for VHF（very high frequency） isolated DCDC converter is proposed.It uses common-gate bootstrapped technique to compensate the power loss due to the threshold voltage,and to solve the reflux problem in the conventional rectifier circuit.As a result,it improves the power conversion efficiency（PCE） and voltage conversion ratio（VCR）.The design saves almost 90%of the area compared to a previously reported double capacitor structure.In addition,we compare the previous rectifier with the proposed common-gate bootstrapped rectifier in the case of the same area;simulation results show that the PCE and VCR of the proposed structure are superior to other structures.The proposed common-gate bootstrapped rectifier was fabricated by using CSMC 0.5 μm BCD process.The measured maximum PCE is 86%and VCR achieves 77%at the operating frequency of 20 MHz.The average PCE is about 79%and average VCR achieves71%in the frequency range of 30-70 MHz.Measured PCE and VCR have been improved compared to previous results.

A VHF RFPGA with adaptive phase-correction technique

This paper presents a VHF（30-300 MHz） RF programmable gain amplifier（PGA） with an adaptive phase correction technique.The proposed technique effectively mitigates phase errors over the VHF band,and the RFPGA as a whole satisfies all the specifications of the China mobile multimedia broadcasting VHF band applications.The RFPGA is implemented with a TSMC 0.25μm CMOS process.Measurement results reveal a gain range of around 61 dB,an ⅡP3 of-7 dBm at maximum gain,a power consumption of 10.2 mA at maximum gain,and a phase imbalance of less than 0.3 degrees.