Guozheng Wang

Technological improvements on the image quality in the low-intensity x-ray real-time imaging system

In this paper, the noise and optical aberration which were two controllable factors that affect the image quality in the single-proximity-focusing x-ray image-intensifier were studied. By decreasing the electron gain of microchannel plate (MCP), the noise of the x-ray image-intensifier can be decreased. The optimal operating condition for the image intensifier and the CCD were also investigated. Based on this investigation, the flash-noise of the x-ray image-intensifier can be decreased and the brightness of the image can be improved. At the end of the paper, some results on the image-capturing of the cool CCD with low noise were presented.

Study of microsphere plate photomultiplier tube

The photomultiplier tube (PMT) that can work in different wavelength is an important detector device in remote sense technology. Microsphere plate using glass beads 50to 70μm in diameter sintered together is the core component of the microsphere plate photomultiplier tube It is a novel two-dimension electron multiplier. The electrons gain for a single plate is about 1017 and do not have the phenomenon of ion-feedback. Furthermore the fabrication process is very easy. In this paper, much interest was put on the microsphere plate photomultiplier tube. Based on the analyses from the theory and the experiment result, we point out the key technology for fabricating PMT is how to obtain glass beads with narrow range in diameter and how to sinter the glass beads with a sufficient pylome. Factors affect the gradating technology and sintering process along with the solution to them is presented. In the last, the structure scheme and technological characteristic for fabricating microsphere plate photomultiplier tube were given. The pulse rising-time of MSP-PMT is below 400ps suitable to the detection of high-speed pulse. As easy to be fabricated and has great advantage over MCP multiplier in the ratio of performance to price, the microsphere plate photomultiplier tube is a promising dim-light detector.

Electrolyte diffusion model in macroporous silicon photo-electrochemical etching and its application in macropore diameter control

In photo-electrochemical etching for macroporous silicon, the electrolyte diffusion in the macropore greatly influences the formation of macroporous silicon, especially the etching rate and macropore diameter. In this study, the electrolyte diffusion was investigated systematically. We focused on the establishment of the electrolyte diffusion model and its impact on the etching rate and macropore diameter. By solving the diffusion equation, the electrolyte diffusion model was deduced, which is different from the commonly accepted model. The main difference is that, in the model, the HF concentration at the macropore tip decreases nonlinearly with macropore length. The module can effectively predict the etching rate. Based on this model, the practical method of etching current density adjustment for fabricating high aspect ratio macroporous silicon was proposed. In addition, the samples were fabricated with a constant etching current density and corrected etching current density. The experimental result indicates that the novel electrolyte diffusion model is practical. The finding from this study shows that the adjustment of etching current density based on the electrolyte diffusion model can effectively control the macropore diameter of high aspect ratio macroporous silicon.In photo-electrochemical etching for macroporous silicon, the electrolyte diffusion in the macropore greatly influences the formation of macroporous silicon, especially the etching rate and macropore diameter. In this study, the electrolyte diffusion was investigated systematically. We focused on the establishment of the electrolyte diffusion model and its impact on the etching rate and macropore diameter. By solving the diffusion equation, the electrolyte diffusion model was deduced, which is different from the commonly accepted model. The main difference is that, in the model, the HF concentration at the macropore tip decreases nonlinearly with macropore length. The module can effectively predict the etching rate. Based on this model, the practical method of etching current density adjustment for fabricating high aspect ratio macroporous silicon was proposed. In addition, the samples were fabricated with a constant etching current density and corrected etching current density. The experimental result in...

Silicon macroporous arrays with high aspect ratio prepared by ICP etching

This paper reports on a macroporous silicon arrays with high aspect ratio, the pores of which are of 162, 205, 252, 276μm depths with 6, 10, 15 and 20 μm diameters respectively, prepared by Multiplex Inductively Coupled Plasma (ICP) etching. It was shown that there are very differences in process of high aspect ratio microstructures between the deep pores, a closed structure, and deep trenches, a open structure. The morphology and the aspect ratio dependent etching were analyzed and discussed. The macroporous silicon etched by ICP process yield an uneven, re-entrant, notched and ripples surface within the pores. The main factors effecting on the RIE lag of HARP etching are the passivation cycle time, the pressure of reactive chamber, and the platen power of ICP system.

Structure release of silicon micro-channel based on wet etching

Based on wet etching theory, the silicon microchannel structure after electrochemical etching was released in TMAH solution to obtain the through-hole microchannel. The silicon wafer with the different resistivity was selected as the substrate of microchannel plate, the TMAH solution was selected in mass concentration of 28.5wt%, and the SiO2 passivation layer with the thickness of 200nm was prepared by thermal oxidation for protection of side-wall of microchannel. Contrary to the problem encountered in wet etching, Firstly, the corrosion characteristics of silicon and SiO2 thin film in TMAH solution were investigated, respectively. In addition, the effects of the pH values of TMAH solution on corrosion characteristics in microstructure releasing of silicon microchannel were studied and analyzed. The experiments show that the silicon wafer with high resistivity can be easily etched, the etching rate of SiO2 film in TMAH is uniform, and adjusting the pH value of etching solution to make it constant during etching can effectively increase the corrosion rate and decrease the surface roughness of samples.

Research on silicon microchannel arrays oxide insulation technology

Silicon microchannel plates (Si-MCP) is widely used in the photomultiplier, night vision, X- ray intensifier and other areas. In order to meet the requirements of high voltage electron multiplier, Si-MCP need to prepare a layer of silicon dioxide in the microchannel to improve the insulating properties. There are many methods for preparing SiO2 layer, such as thermal growth, magnetron sputtering method and chemical vapor deposition etc. The thermal oxidation method is often used for preparation of insulating layer that it grows film thickness uniformity, compact structure, simple process and so on. There will be bending deformation phenomenon of silicon microchannel arrays in high temperature oxidation process. The warpage of Si-MCP has brought great for difficulties of subsequent processing. Silicon crystals has the properties of plastic deformation at high temperature, this article take full advantage of this properties by which the already bending deformation of silicon microchannel arrays can be restored to flat.

Research on resistance properties of conductive layer materials of microchannel plate film dynode

Silicon Microchannel Plate（MCP）is a new image multiplier devices based semiconductor process technology. Compared with the traditional glass MCP, Silicon MCP has an advantage in technology that the dynode materials and the substrate materials are separate. At the same time, the dynode preparation process and the microchannel arrays are also separate. Two different dynode conductive layer films are prepared: polysilicon conductive films prepared by low pressure chemical vapor deposition (LPCVD) and AZO thin films coated by atomic layer deposition (ALD). The conductive films coated by ALD are superior to dynode conductive films prepared by LPCVD. By comparing the resistivity of conductive polysilicon thin film and AZO thin film of different Al concentrations doped, AZO thin film of different Al concentrations doped is a more suitable conductive layer dynode material to satisfy the MCP conductive layer resistivity requirements.

Influence of surfactant on aperture of photo-electro-chemical etching for silicon microchannel plate

The influence of several surfactants in electrolyte during silicon electrochemical etching was reported in this paper. The morphologies of macroporous silicon arrays in n-type silicon are strongly influenced by the chemical nature of these additives. Conventional solvents (HF-Ethanol) with cationic (hexadecyl trimethyl ammonium chloride), non-ionic (Triton-X100) and anionic (sodium alpha-olefin sulfonate) surfactants were experimented respectively. Prominent differences in microchannel morphologies and apertures were observed depending on the nature of the additive. The different behaviors of the additives during the electrochemical etching process were linked to the physical properties of the additives. We found the electric double layer model of the reaction interface partially to explain these results. However, not only the morphology of the microchannel but also the degree of electrochemical reaction is affected by surfactant. The anionic surfactant is more suitable for the preparation of silicon microchannel plate with high aspect ratio and pore size uniform. The depth of microchannels etched by photoelectrochemical etching silicon with anionic surfactant is 264 μm, and the pore size is 2 μm.

Influences of temperature and etching voltage on the surface morphology of photo-electro-chemical etching for silicon microchannel arrays

The application fields of high aspect ratio Si microchannel arrays have increased considerably, for example, Si microchannel plates, MEMS devices and so on. By the method of photo-electrochemical etching (PEC), Si microchannel arrays are prepared using n-Si wafer covered by anti-corrosion layers and initiation array pits. The dark current intensity curve of an n-type silicon wafer was presented in aqueous HF. The relationship among temperature, etching voltage and carrier transportation was presented. The influences of temperature and etching voltage on the surface morphology of silicon microchannel arrays were researched. The perfect Si microchannel arrays structure with the pore depth of 297 μm, the pore size of 3 μm and the aspect ratio of 99 was obtained by the method of reducing etching voltage gradually.

Research on Silicon Microchannel Array Oxidation Insulation Technology and Stress Issues

Microchannel plate is widely used in the field of low light level night vision, photomultiplier, tubes, X-ray enhancer and so on. In order to meet the requirement of microchannel plate electron multiplier, we used the method of thermal oxidation to produce a thin film of silicon dioxide which could play a role in electric insulation. Silicon dioxide film has a high breakdown voltage, it can satisfy the high breakdown voltage requirements of electron multiplier. We should find the reasonable parameter values and preparation process in the oxidation so that the thickness and uniformity of the silicon dioxide layer would meet requirement. This article has been focused on researching and analyzing of the problem of oxide insulation and thermal stress in the process of production of silicon dioxide film. In this experiment, dry oxygen and wet oxygen were carried out respectively for 8 hours. The thickness of dry oxygen silicon dioxide films was 458 nm and wet oxygen silicon dioxide films was 1.4 μm. Under these conditions, the silicon microchannel is uniformity and neat, meanwhile the insulating layers breakdown voltage was measured at 450 V after the wet oxygen oxidation. By using ANSYS finite element software, we analyze the thermal stress, which came from the microchannel oxygen processes, under the conditions of which ambient temperature was 27 ℃ and porosity was 64%, we simulated the thermal stress in the temperature of 1200 ℃ and 1000 ℃, finally we got the maximum equivalent thermal stress of 472 MPa and 403 MPa respectively. The higher thermal stress area was spread over Si-SiO2 interface, by simulate conditions 50% porosity silicon microchannel sample was selected for simulation analysis at 1100 ℃, we got the maximum equivalent thermal stress of 472 MPa, Thermal stress is the minimum value of 410 MPa.