Experimental Study on Wax Protective Coating for Wet Deep Silicon Etching Processes

In order to protect the finished structures on the front side during deep silicon wet etching processes, the wax coating for double-sided etching process on the wafer is studied to separate the aforementioned structures from the strong aqueous bases. By way of heating and vacuumization, the air bubbles are expelled from the coating to extend the protection duration. The air pressure in the sealed chamber is 0.026 7 Pa, and the temperature of the heated wafer is 300℃. Two kinds of the wax are used, and the corresponding photos of the etched wafer and the protection times are given. In 75 ℃ 10 % KOH solution, the protection duration is more than 8 h.

Fabrication of High-Density Out-of-Plane Microneedle Arrays with Various Heights and Diverse Cross-Sectional Shapes

Out-of-plane microneedle structures are widely used in various applications such as transcutaneous drug delivery and neural signal recording for brain machine interface.This work presents a novel but simple method to fabricate high-density silicon(Si)microneedle arrays with various heights and diverse cross-sectional shapes depending on photomask pattern designs.The proposed fabrication method is composed of a single photolithography and two subsequent deep reactive ion etching(DRIE)steps.First,a photoresist layer was patterned on a Si substrate to define areas to be etched,which will eventually determine the final location and shape of each individual microneedle.Then,the 1st DRIE step created deep trenches with a highly anisotropic etching of the Si substrate.Subsequently,the photoresist was removed for more isotropic etching;the 2nd DRIE isolated and sharpened microneedles from the predefined trench structures.Depending on diverse photomask designs,the 2nd DRIE formed arrays of microneedles that have various height distributions,as well as diverse cross-sectional shapes across the substrate.With these simple steps,high-aspect ratio microneedles were created in the high density of up to 625 microneedles mm^(-2)on a Si wafer.Insertion tests showed a small force as low as~172μN/microneedle is required for microneedle arrays to penetrate the dura mater of a mouse brain.To demonstrate a feasibility of drug delivery application,we also implemented silk microneedle arrays using molding processes.The fabrication method of the present study is expected to be broadly applicable to create microneedle structures for drug delivery,neuroprosthetic devices,and so on.

Above 700 V superjunction MOSFETs fabricated by deep trench etching and epitaxial growth

Silicon superjunction power MOSFETs were fabricated with deep trench etching and epitaxial growth,based on the process platform of the Shanghai Hua Hong NEC Electronics Company Limited.The breakdown voltages of the fabricated superjunction MOSFETs are above 700 V and agree with the simulation.The dynamic characteristics, especially reverse diode characteristics,are equivalent or even superior to foreign counterparts.

Subtle Variations in Surface Properties of Black Silicon Surfaces Influence the Degree of Bactericidal Efficiency

One of the major challenges faced by the biomedical industry is the development of robust synthetic surfaces that can resist bacterial colonization. Much inspiration has been drawn recently from naturally occurring mechano-bactericidal surfaces such as the wings of cicada(Psaltoda claripennis) and dragonfly(Diplacodes bipunctata) species in fabricating their synthetic analogs. However,the bactericidal activity of nanostructured surfaces is observed in a particular range of parameters reflecting the geometry of nanostructures and surface wettability. Here,several of the nanometer-scale characteristics of black silicon(bSi) surfaces including the density and height of the nanopillars that have the potential to influence the bactericidal efficiency of these nanostructured surfaces have been investigated. The results provide important evidence that minor variations in the nanoarchitecture of substrata can substantially alter their performance as bactericidal surfaces.

Statistical key variable analysis and model-based control for improvement performance in a deep reactive ion etching process

This paper proposes to develop a data-driven via＇s depth estimator of the deep reactive ion etching process based on statistical identification of key variables.Several feature extraction algorithms are presented to reduce the high-dimensional data and effectively undertake the subsequent virtual metrology（VM） model building process.With the available on-line VM model,the model-based controller is hence readily applicable to improve the quality of a via＇s depth.Real operational data taken from a industrial manufacturing process are used to verify the effectiveness of the proposed method.The results demonstrate that the proposed method can decrease the MSE from 2.2×10^（-2） to 9×10^（-4） and has great potential in improving the existing DRIE process.

Fabrication of high-voltage light emitting diodes with a deep isolation groove structure

In order to connect several independent LEDs in series, inductively coupled plasma （ICP） deep etching of GaN is required for isolation. The GaN-based high-voltage （HV） LEDs with a 5 μm deep isolation groove and an acceptable mesa sidewall angle of 79.2° are fabricated and presented. The surface morphology and construction profile of the etched groove are characterized by laser microscopy and scanning electron microscopy. After contact metal formation and annealing, the electrical properties are evaluated by I-V characteristics. The trend of the I-V curve has good accordance with conventional LEDs. The contact resistance of HV LEDs is also tested and was reduced by 4.6 Ω compared to conventional LEDs, while the output power increased by 5 W. The results show that this technique can be applied to practical fabrication.

A review:crystalline silicon membranes over sealed cavities for pressure sensors by using silicon migration technology

A silicon pressure sensor is one of the very first MEMS components appearing in the microsystem area.The market for the MEMS pressure sensor is rapidly growing due to consumer electronic applications in recent years. Requirements of the pressure sensors with low cost, low power consumption and high accuracy drive one to develop a novel technology. This paper first overviews the historical development of the absolute pressure sensor briefly. It then reviews the state of the art technology for fabricating crystalline silicon membranes over sealed cavities by using the silicon migration technology in detail. By using only one lithographic step, the membranes defined in lateral and vertical dimensions can be realized by the technology. Finally, applications of MEMS through using the silicon migration technology are summarized.