Electron Beam Writer Enables Microfabrication

University of California, San Diego

The new electron beam writer housed in the cleanroom facility at the Qualcomm Institute, previously the UCSD division of the California Institute of Telecommunications and Information Technology, is important for two major areas of research by Shadi Dayeh, PhD, an electrical and computer engineering professor. He is developing next-generation, nanoscale transistors for integrated electronics. At the same time, he is working to develop neural probes that can extract electrical signals from brain cells and transmit the information to a prosthetic device or computer. To achieve this level of signal extraction or manipulation requires tiny sensors spaced very closely together for the highest resolution and signal acquisition. Enter the new electron beam writer. (See Figure 1)

Fig. 1 – Ryan Anderson, a process engineer for the Nano3 facility in the Qualcomm Institute, prepares to remove a sample from the Vistec EBPG5200 electron beam writer. (Credit: UC San Diego Jacobs School of Engineering.)

Electron beam (e-beam) lithography enables researchers to write very small patterns on large substrates with a high level of precision. Applications range from writing patterns on silicon and compound semiconductor chips for electronic device and materials research to genome sequencing platforms. In an ebeam writer, unique patterns are “written” on a silicon wafer coated with a polymer resist layer sensitive to electron irradiation. The machine directs a narrowly focused electron beam onto the surface marking the pattern, making parts of the resist coating insoluble and others soluble. The soluble area is later washed away, revealing the pattern, which can have sub-10 nanometer feature dimensions.

Bioengineering professor Todd Coleman, PhD, uses the e-beam writer in building epidermal electronic devices. The electronic tattoos are designed to acquire brain signals for a variety of medical applications, from monitoring infants for seizures in neonatal intensive care to studying cognitive impairment associated with Alzheimer’s disease.

Dayeh said the e-beam writer will allow the university to conduct research under President Obama’s BRAIN Initiative, which requires developing smaller sensing and stimulating elements with higher resolution on chips the size of a few millimeters. “Current state-of-the-art electro-neural interfacing technology enables sensing from hundreds or thousands of neurons. If you want to understand the neurophysiology on the individual cell basis, then we need to develop sensors that have the spacing of a few tens of nanometers, which is about one-hundredth the size of a neuron and is on the same scale as their synaptic connections,” he said.