diamond‐like coating
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2019-04-01 |
| Journal | Electronics Letters |
| Authors | Anonymous |
Abstract
Section titled “Abstract”Researchers from the Key Lab of MEMS of Ministry of Education and Quantum Information Research Center, Southeast University, have investigated a novel micro-printing process which uses anodic bonding to deposit patterned diamond-like carbon (DLC) coatings on glass. Characterisation of the produced coatings demonstrates a variety of designs that can be successfully fabricated with high optical transparency in the IR spectral range. Micro-printing is the production of recognisable patterns or characters in a printed medium at a scale that requires magnification to read with the naked eye. DLC coating is a class of amorphous carbon coating that exhibits some of the typical properties of diamond. Besides low cost DLC patterning, the micro-printing technology reported may also be useful for other film coating including aluminum, copper, etc. High optical transparency in the infrared spectral range makes DLC coatings on glass substrates suitable for optical devices, infrared cameras, solar cells, and LEDs; to name just some of the possible commercial applications. Micro-printing of patterned DLC coatings on glass wafers is also applicable in optical MEMS devices and deepens the understanding of plasma discharge in anodic bonding processes (a wafer bonding process for sealing together silicon or metal with no intermediary layer), useful for device fabrication, device packaging and printing with other materials. PhD candidates Yu Ji and Jin Zhang from Prof. J. Shang’s group holding up a bonding wafer with patterned diamond-like carbon coatings in the cleanroom at MEMS lab/Quantum Information Research Center of Southeast University. Photographs of DLC-coated glass substrates with various patterns. In general, oxygen generation and plasma discharge are negative effects during anodic bonding. For the first time, plasma discharge during anodic bonding is taken as a positive effect to deposit patterned diamond like carbon coatings on glass wafers. Co-author Professor Shang outlines the novel micro-printing process: “It consists of the following steps sequentially: (1) through-hole cavities with various patterns such as squares, triangles and letters are fabricated on a silicon wafer; (2) a glass wafer, the silicon wafer and a graphite wafer are stacked vertically; (3) anodic bonding is conducted under the conditions of 350°C and 800 Volts. When O2 gas breakdown occurs, graphite in the cavities is bombarded and carbon atoms sputtered from the graphite are rearranged to form patterned DLC coatings on the glass wafer.” The patterned DLC coatings are subsequently characterised by Raman spectroscopy, atomic force microscopy (AFM) and an ultraviolet spectrophotometer. Results show that the patterned DLC coatings have a surface roughness of 1.21 nanometres in the scanning area of 5×5 micrometres. The ratio of light energy impinging on a body to that transmitted through it (the transmittance) of the DLC-coated glass wafer is above 85%, indicating that the patterned DLC coatings have high optical transparency in the IR spectral range. Many methods, such as chemical vapor deposition (CVD), pulsed laser deposition (PLD), and ion-beam deposition and sputtering, have been developed for the deposition of DLC coatings on glass substrates. Followed by lithography and reactive ion etching, patterned DLC coatings are formed. Different from these techniques, this work presents a novel technique to micro-print patterned DLC coatings on glass wafers by anodic bonding. For the first time, plasma discharge is used to deposit patterned DLC coatings on glass wafers. This research will develop a new area of in-cavity coating by anodic bonding. Before, patterned coatings had to be fabricated by deposition, lithography and reactive ion etching. Using this method, the deposition process of patterned DLC coatings only has a single step. Initially, the group used wet etching to form through-hole cavities with various patterns such as squares, triangles and letters in a silicon wafer. However, the shapes of the patterns were irregular after wet etching. The team soon struck on fabricating the through-hole cavities with laser drilling (LPKF ProtoLaser U3). In the short term, this work deepens understanding of plasma discharge in anodic bonding processes and is useful for device fabrication and device packaging by anodic bonding. In the long term, this research will help develop a new area of in-cavity coating by anodic bonding for not only DLC coatings but also other, possibly metallic materials. “We plan to micro-print other patterned coatings such as aluminum, aluminium oxide，graphene on glass wafers.”, says Professor Zhang, continuing: “To control the quality of patterned DLC coatings, we are conducting an exploration into the parameter spaces of bonding temperature, bonding voltage, bonding time and even distance between graphite wafer and glass. In addition to this, other patterned metal film production can be attempted using this method.” In the next decade, with the development of the internet of things (IOT) and intelligent cars, MEMS devices will become smaller and smarter, and the packaging and integration of MEMS devices will increase in importance. Anodic bonding as a major method for device fabrication and device packaging can be widely applied in these industry applications. For such applications, plasma discharge prevention will entail careful anodic bonding process design. This research could develop a new area of in-cavity coating by anodic bonding, where cavity size will be controlled on nanometre to centimetre scales.