PCB Design MOEMS Devices and Technologies PCB Design MOEMS devices are classified into interference, diffractive, transmissive, and reflective types according to their physical working principle (see Table 1). Most of them use reflective devices. MOEMS has achieved significant development over the past few years. In recent years, due to the increase in demand for high-speed communications and data transmission, the development of MOEMS technology and its devices has been greatly stimulated. A low-loss, low-EMV sensitivity, low crosstalk, high data rate reflective optical PCB design MOEMS device has been developed.
Today, in addition to simple devices such as variable optical attenuators (VOAs), tunable vertical cavity surface emitting lasers (VCSELs), optical modulators, and tunable wavelength selective photodetectors can also be fabricated using MOEMS technology. Active devices and filters, optical switches, programmable wavelength optical add/drop multiplexers (OADM) and other optical passive devices and large-scale optical cross-connect (OXC).
In information technology, one of the keys to optical applications is commercial light sources. In addition to monolithic light sources (such as thermal radiation sources, LEDs, LDs, and VCSELs), MOEMS light sources with active components are of particular interest. For example, in a tunable VCSEL, the wavelength of its emission can be changed by changing the length of the resonator by micromechanics, thereby realizing high-performance WDM technology. Currently, support cantilever tuning methods and active structures with support arms have been developed.
MOEMS optical switches with movable mirrors and mirror arrays have also been developed for assembling OXC, parallel and On/Off switch arrays. Figure 2 shows a free space MOEMS fiber optic switch with a pair of U-shaped cantilever actuators for lateral movement of the fiber. Compared with the conventional waveguide switch, the advantages are lower coupling loss and less crosstalk.
A continuously adjustable optical filter with a wide range is a very important device in a variable DWDM network, and MOEMS F_P filters using various material systems have been developed. Due to the mechanical flexibility of the adjustable diaphragm and effective cavity length, these devices have a wavelength tunable range of only 70 nm. Japan's OpNext Corporation has developed a MOEMS F_P filter with a recordable tunable width. The filter is based on multiple InP/air-gap MOEMS technology. The vertical structure consists of six layers of suspended InP diaphragms. The film has a circular structure and is supported by three or four suspension supports and is respectively associated with three or four. Rectangular support table connection. The continuous tunable F_P filter has a very wide stop band, covers the second and third optical communication windows (1 250 to 1800 nm), has a wavelength tuning width greater than 11 2 nm, and an actuation voltage as low as 5V.
MOEMS Design and Production Technology Most MOEMS production technologies evolve directly from the IC industry and its manufacturing standards. Therefore, body and surface micromachining and high-throughput micromachining (HARM) technology are used in MOEMS. But there are other challenges such as die size, material uniformity, 3D technology, surface topography, and final processing, roughness, and temperature sensitivity.
Lithography is widely used to make structural graphics. In addition, maskless lithography can also be used to make conventional graphics. For example, the surface of a photosensitive material such as a polymer. In order to obtain a low-refractive-index surface, a two-dimensional pattern can also be produced, which can replace a conventional multi-layer antireflection coating and can be used in MOEMS to improve its performance. The materials used and their deposition techniques are similar to standard IC processes such as Si thermal oxidation, LPCVD, PECVD, sputtering, electroplating, etc. Different types of wet etching and dry etching techniques may also be used. For example, SiV-shaped grooves can be very precisely formed by wet anisotropic etching, and are widely used for the alignment and packaging of optical fibers and optoelectronic devices. Micromirrors can be fabricated by wet reactive ion etching (DRIE) and surface micromachining. With the fine honing technique, a non-planar structure having a large longitudinal mode ratio can also be obtained.
At present, the most used method is the micromachined silicon wafer planar technology with chip solder bumps, which makes standard and low-cost IC assembly methods possible. To protect the chip, the wafer plane can be closed by a gel coat, and a groove-like flow soldering method (IRS) can be used as a method of improving a wafer-level package. Some new MOEMS products are particularly sensitive to temperature. Leaded devices are typically hand soldered, while surface mount devices are laser soldered.
Successful technologies such as analog feedback loop (FEA), process optimization, and secondary design have been used in MOEMS. In addition to mechanical, thermal, and electrical simulations, light simulation (BPM) and performance characterization were also introduced. In addition, due to the high optical alignment requirements, packaging technology has been introduced in the design simulation in order to achieve complete optical device packaging and interconnection requirements. Figure 3 shows the MOEMS design simulation and technical process program.
MOEMS Packaging Technology In addition to developing practical PCB design MOEMS devices, the main challenge is to assemble and package reliable devices in dedicated packages. Although many devices have been developed, there are few devices that can reliably operate in the market. One of the reasons is the difficulty in packaging and the difficulty in achieving reliable, low-cost optical links. In particular, as PCB design MOEMS devices enter the application field, the main problem is light alignment and packaging. In addition, the actual loss of PCB design MOEMS devices also depends on the packaging technology.
Different from the standard package method, the MOEMS components and packages are special applications. Because each MOEMS device design is a non-standard development, and different applications have different packaging requirements, the MOEMS production technology is mainly package technology, and the packaging cost is MOEMS. The largest proportion of the total system cost is 75%-95%. So there are developers who say: Packaging is a process, not a science.
MOEMS package is generally divided into chip-level, device-level, system-level three. The chip-scale package includes chip passivation, isolation and soldering, providing power path, signal conversion and interconnection leads, and passivation protection and isolation of sensing elements and actuators; device-level packaging including signal measurement and conversion, leads Bonding and component soldering; system-level packaging includes packaging, juice, fabrication, assembly, and testing. 2 x 2 optical switch package with glass fiber and ball lens. This high-performance, low-wattage, mass-producable MOEMS optical switch meets all optical network requirements for devices.