Electroplating in micro/nano fabrication is an important MEMS manufacturing technology. It is widely used for forming metal microstructures, fabricating interconnects and preparing sensor electrodes. As MEMS chips move toward higher integration and more complex structures, precision control at the micro/nano scale becomes increasingly critical. This article introduces the core technologies, process flow and MEMS applications of micro/nano electroplating.
Electroplating is an electrochemical deposition technique used to form metal films on a substrate surface. In micro/nano fabrication, electroplating is mainly used for the following purposes:
Compared with conventional electroplating, micro/nano electroplating places greater emphasis on high-aspect-ratio filling capability, nanometer-scale thickness control, deposition uniformity and stress management.
Lithography-based electroplating. In this route, photoresist is first spin-coated onto a silicon or glass substrate, and lithography is used to form a microstructure mold. Metals such as copper, nickel or gold are then electroplated inside the mold. After the resist is removed, the required metal microstructure is obtained. This method is commonly used for RF MEMS switches, micro coils and microelectrode arrays.
LIGA and micro-electroforming. LIGA combines X-ray lithography, or UV lithography in some cases, with electroplating to manufacture high-aspect-ratio metal microstructures. Typical materials include nickel, copper and gold. It is used for micro gears, micro actuators and molds for microfluidic chips.
TSV electroplating. TSV electroplating is used for vertical interconnection in three-dimensional integrated circuits. Pulse plating or additive-assisted plating is often adopted. Key challenges include void-free filling and low-stress deposition.
Nano-electroplating. By controlling current density, additives and other parameters, nano-electroplating can achieve nanoscale metal deposition. Typical applications include nanowires, quantum dot devices and high-precision sensors.
| Key Parameter | Optimization Objective | Typical Method |
|---|---|---|
| Current density | Uniform deposition | Pulse plating and reverse pulse plating |
| Bath composition | Defect reduction | Additives such as brighteners and levelers |
| Temperature control | Improved adhesion | Constant-temperature plating bath |
| Agitation method | Enhanced mass transfer | Ultrasonic assistance or microfluidic circulation |
MEMS inertial sensors. Electroplated nickel or gold microstructures can be used for movable proof masses and electrodes in accelerometers and gyroscopes, improving mechanical strength and signal sensitivity.
RF MEMS. Electroplated gold microbridge structures are used in high-frequency switches to reduce resistance loss.
Microfluidic chips. Copper or nickel microchannel molds can be fabricated by electroplating and then used for PDMS replication.
Bio-MEMS. Electroplated gold microelectrode arrays can be used for biological signal detection.
Future development will include three-dimensional electroplating for more complex MEMS structures such as multilayer microactuators, nanocomposite electroplating with carbon nanotubes or graphene to enhance conductivity, and greener electroplating processes that reduce the use of toxic chemicals, such as cyanide-free gold plating.
Electroplating is one of the core technologies in MEMS manufacturing. Its high precision and controllability make it irreplaceable in sensors, RF devices, biochips and other applications. With advances in new electroplating technologies and materials, micro/nano electroplating will continue to support MEMS chips with higher performance and smaller dimensions.
