​Advanced Interconnects

         ​Interconnect is a network of wirings in integrated circuit chips, which connects and enables the communication between transistors in an integrated circuit (IC). Copper became the material of choice for interconnects in semiconductor industry a couple of decades ago because of its superior conductivity and reliability. As the semiconductor technology rapidly evolves the future devices requires new interconnect materials to meet the device performance. In addition, other emerging devices such as quantum computers demands new materials for their unique operation requirements. 

Our group is exploring the electrodeposition of alternative metals and the impacts of different chemistries on the properties of metal deposits. The aim of our research in this topic is to enable the fabrication of advanced interconnects to meet the requirements of future devices.

Superconducting Metals for Quantum Devices

Superconductive circuits are critical for the cryogenic quantum devices because such circuits avoid electrical thermal effects and prevent thermal perturbation to the quantum device. Our group is investigating a new type of aqueous electrolytes, “water-in-salt”, for the electrodeposition of rhenium for its superconductivity. While being aqueous, the free water molecules in such electrolytes are depleted upon the hydration of a super-high concentration of salt. This special characteristics suppresses the electrochemical reactions of water molecule and associated species such as proton and hydroxide anions, while maintaining the advantages of an aqueous solution.

Rhenium films electrodeposited from a electrolyte containing a high concentration of LiCl showed significantly mitigated film cracks and improved film roughness. Furthermore, the superconducting critical temperature increased from the bulk value, 1.7 K, to 6 K for electrodeposited amorphous Re. We aim to understand the impacts of water-in-salt electrolytes on electrodeposition processes, and the mechanisms for their impacts on the superconductivity of deposited films. 

​Electrochemical 3D “Printing”

3D printing is a new way of fabricating structures in a layer by layer fashion or a so called bottom-up way. It is particularly useful for complex structures that cannot be made with the traditional machining (top down) approach or can only be made with a very high cost. While 3D printing typically focuses on the manufacturing of large objects such as mechanical parts, we are exploring metal 3D printing using local electrochemical deposition for structures below millimeters.

By controlling the distribution of organic additives that control the electrochemical growth of metals, localized growth can be achieved. Our study focuses on the effects of chemistry and process on the controllability of such growth, as well as the properties of printed free-standing structure. The purpose of study is to enable the rapid, scalable and low cost manufacturing of micro-electro-mechanical system (MEMS) and nano-electro-mechanical system (NEMS). 

​Electrochemical Deposition of Chalcogenides

Apart from metals, which electrochemical processes have long demonstrated to be capable of depositing, we are exploring the electrodeposition of semiconductor materials, including chalcogenide compounds. We are interested in this type of materials for their semiconducting, magnetic, phase change and piezoelectric properties. Our study focuses on the nucleation of chalcogenides and how the material changes at such initial stage of growth. We are also interested in the direct formation of chalcogenide 3D structures for device fabrication using the electrochemical 3D printing process we are exploring.

​Electrochemical Interfacial Resistive Memory

Multi-level resistive memory​ is of great interest for neuromorphic circuits, where the multiple resistance levels can be used to mimic the memory behavior of biological brain. We are exploring a liquid phase, low bias, multi-level resistive memory behavior based on electrochemical interfacial resistance. The reversible change of the interfacial resistance as well as the multiple resistance levels upon the “writing” with a series of electrical pulses have been demonstrated. Our studies are focused on understanding the mechanism behind such behaviors and on how to improve the controllability or repeatability of the multiple levels of operation.