Futing Yi

Fabrication and antireflection properties of solar cells with pyramid-nanohole texture by caesium chloride lithography

Pyramids and nanoholes are integrated together to form a micro-nano-texture on silicon surface in order to suppress reflection for silicon solar cell application. The nanoholes are formed by inductively coupled plasma (ICP) dry etching employing a nanoporous aluminum (Al) mask which is fabricated by caesium chloride (CsCl) nanoislands lift-off technique. Reflection of less than 4% can be reached by pyramid-nanohole texture, which is much lower than that from pure pyramids or nanoholes texture. Higher short circuit current density (J(sc)) and photovoltaic conversion efficiency (PCE) are obtained for the solar cell with pyramid-nanohole texture due to its better antireflection. The average diameter and depth of the nanoholes affect the solar cell properties. The smaller and deeper nanoholes can suppress reflection a lot, but meanwhile, the formation of them means more crystal lattice defects generated from ICP etching. An optimized diameter of 800 nm and depth of 1 mu m for the nanoholes are obtained in our experiments to get the best photovoltaic performance that is a PCE of 14.89% with a J(sc) of 38.25 mA cm(-2) and an open circuit voltage (V-oc) of 544.8 mV.

The Fabrication and Photoelectric Properties of the Nanopillar Arrays for Solar Cell

a method combining Csesium Chloride (CsCl) self-assembly and inductively coupled plasma (ICP) etching has been used to fabricate nanopillars with high aspect ratio structures on sillicon wafer. The silicon surface with nanopillars of average diameter 350nm and aspect ratios 4, like black wafer, has very low reflectivity at a width of light spectrum. After diffusion of phosphorus (P) and passivation of SiO2 layer on the pillars surface, the reflectivity has been reduced more to below 3% for wavelength from 400nm to 800nm, which could meet the requirement of antireflection for solar cells. What’s more, the reflectivity of nanopillar surface could not obey the formula of reflection to increase with the incident angle of light like planar, and has almost unchanged small values at incident angle of 10°-50°. The solar cell with nanopillars has been fabricated with thermal diffusion of P, chemical deposion of Cu electrode with UV lithography. Its I×V output power of photoelectric property has been measured with sunlight at different time in one day corresponding to different incident angle, and measure of common solar cell is done at the same time for comparation. In order to select the inflection factor of incident angle, the data of output power have been united by dividing max value for nanopillar and common solar cells individually. The united curve of nanopillars cell shows obviously larger value than that of common cell at above incident angle of about 15°, which means nanopillars cell could have the potential ability to offer more electric energy production daily than that of common solar cell.

Fabrication of silicon nanotip arrays with high aspect ratio by cesium chloride self-assembly and dry etching

Nanotip arrays with high aspect ratio, which have attracted much attention due to their potential applications, have been fabricated by many methods. Dry etching combined with self-assembly masks is widely used because of the convenience of dry etching and high throughput of self-assembly. In this paper, we report a method combining Cesium Chloride (CsCl) self-assembly with inductively coupled plasma (ICP) dry etching to fabricate silicon nanotip arrays with high aspect ratio and silicon nanotip arrays with aspect ratio 15 have been achieved after optimization of all parameters.

Dynamic properties of a metal photo-thermal micro-actuator

This work presents the design, modeling, simulation, and characterization of a metal bent-beam photo-thermal micro-actuator. The mechanism of actuation is based on the thermal expansion of the micro-actuator which is irradiated by a laser, achieving noncontact control of the power supply. Models for micro-actuators were established and finite-element simulations were carried out to investigate the effects of various parameters on actuation properties. It is found that the thermal expansion coefficient, thermal conductivity, and the geometry size largely affected actuation behavior whereas heat capacity, density, and Youngs modulus did not. Experiments demonstrated the dynamic properties of a Ni micro-actuator fabricated via LIGA technology with 1100/30/100 μm (long/wide/thick) arms. The tip displacement of the micro-actuator could achieve up to 42 μm driven by a laser beam (1064 nm wavelength, 1.2 W power, and a driving frequency of 1 HZ). It is found that the tip displacement decreases with increasing laser driving frequency. For 8 Hz driving frequency, 17 μm (peak-valley value) can be still reached, which is large enough for the application as micro-electro-mechanical systems. Metal photo-thermal micro actuators have advantages such as large displacement, simple structure, and large temperature tolerance, and therefore they will be promising in the fields of micro/nanotechnology.

Large-aperture prism-array lens for high-energy X-ray focusing

A new prism-array lens for high-energy X-ray focusing has been constructed using an array of different prisms obtained from different parabolic structures by removal of passive parts of material leading to a multiple of 2π phase variation. Under the thin-lens approximation the phase changes caused by this lens for a plane wave are exactly the same as those caused by a parabolic lens without any additional corrections when they have the same focal length, which will provide good focusing; at the same time, the total transmission and effective aperture of this lens are both larger than those of a compound kinoform lens with the same focal length, geometrical aperture and feature size. This geometry can have a large aperture that is not limited by the feature size of the lens. Prototype nickel lenses with an aperture of 1.77 mm and focal length of 3 m were fabricated by LIGA technology, and were tested using CCD camera and knife-edge scan method at the X-ray Imaging and Biomedical Application Beamline BL13W1 at Shanghai Synchrotron Radiation Facility, and provided a focal width of 7.7 µm and a photon flux gain of 14 at an X-ray energy of 50 keV.

Research Survey of Electroformed Nickel Material Properties Used in MEMS

As one of the significant structural materials used in safe and arming system of MEMS fuze, the research on micro-electroforming process technologies and micro-electroforming nickel’s properties have been a popular field for MEMS area. This paper surveys present domestic and overseas research status of mechanical characterization of electroformed nickel, summarizes and analyzes that changes of the microstructure led by parameters of micro-electroforming process and the external environment make great effects.

The application of multilayer elastic beam in MEMS safe and arming system

In this paper, a new approach for a multilayer elastic beam to provide a driving force and driving distance for a MEMS safe and arming system is presented. In particular this is applied where a monolayer elastic beam cannot provide adequate driving force and driving distance at the same time in limited space. Compared with thicker elastic beams, the bilayer elastic beam can provide twice the driving force of a monolayer beam to guarantee the MEMS safe and arming systems work reliably without decreasing the driving distance. In this paper, the theoretical analysis, numerical simulation and experimental verification of the multilayer elastic beam is presented. The numerical simulation and experimental results show that the bilayer elastic provides 1.8–2 times the driving force of a monolayer, and a method that improves driving force without reducing the driving distance.

The Fabrication of Silicon Nanopin with CsCl Nanoislands and Dry Etching for Field Emission

Silicon nano pin arrays with heights of 1.3-3.66um and diameter of 315-899nm, are fabricated by CsCl self-assemble for CsCl nano islands for mask and ICP etching for silicon pins. CsCl film is firstly deposited on the wafer by thermal evaporation and putted in the humid controlled environment to be developed to the CsCl islands with diameter of 341-915 nm as self-assembled technology. Then the ICP etching with SF6, CCl4, He gas is introduced to make the silicon nano pin by the mask of CsCl nano islands, and the silicon nano pins with the different height of 1.3-3.66 um are finished for field emission. The gated FEA templates are fabricated by photolithography process and the lift-off technology with Ti-Si film as the gate electrodes. The final template for field emission has the silicon nano pins with diameters of 31.7 nm on top, Ti-Ag film with thickness of 105nm and gate holes of 30um in diameter, and SU8 resist insulator structure with thickness of 4um and holes of 10um in diameter. The optimization of the fabrication process and the performance for the configuration will be made.

Photothermal Microactuators Fabricated by LIGA Technology

A novel microactuator based on photothermal expansion is introduced, which is actuated by laser beam eliminating external circuit. The mechanism of the photothermal expansion is theoretically analyzed, and the working principle of a U-shaped photothermal microactuator with two arms is introduced and the lateral deflection is calculated. LIGA technology involving X-ray lithography and electroplating is introduced to fabricate photothermal microactuators. The fabrication process with LIGA technology is introduced and important details such as X-ray mask and electroplating are discussed. Photothermal microactuators with different structures are fabricated by LIGA technology at Beijing Synchrotron Radiation Facility (BSRF) and tests are carried out with laser beam. The deflection of a V-shaped photothermal microactuator of Ni material can reach 25.8 μm under the control of a 1064 nm, 800 mW laser and a U-shaped can reach about 11 μm at an 808 nm, 600 mW laser.