Voltage Controlled Laser Scribed Graphene (LSG) Microstrip Attenuator

Abstract

In this paper, a preliminary design of a voltage-tunable microstrip attenuator using Laser Scribed graphene (LSG) is proposed. The paper will demonstrate that the fabrication of LSG from graphene oxide on standard doubled-sided FR-4 Copper-clad Substrate can be used as a voltage-controlled resistor that results in a tunable microstrip attenuator across the microwave frequencies from 50MHz to 5.5GHz. The measured attenuation ranges from 2.6 dB to 11.5dB at 4 GHz with a DC bias voltage ranging from 0V (minimum attenuation) to 6.0V (maximum attenuation). Graphene is a unique material with interesting electromagnetic and mechanical properties. Graphene conducts electricity better than copper and rapidly dissipates heat, making it useful for many applications. Large-scale production of graphene has been made possible for applications such as printable electronics and electrodes for Supercapacitors and has started to gain interest for use in microwave circuits; however, traditional methods of creating graphene involve many chemical steps and are costly for microwave circuits. Removing oxygen from graphene oxide to obtain high-quality graphene has been a major challenge over the past two decades for the scientific community due to how oxygen distorts the pristine atomic structure of graphene and degrades its properties. A study some time ago, done by researchers at UCLA, introduced a novel way of making graphene [1]. The research used direct laser writing of graphene electronics with a consumer grade LightScribe DVD burner for the synthesis, patterning, and writing of graphene electronics from a graphite oxide source to create electrodes for supercapacitors [2]. The laser will resonate with the natural frequency of the graphene and oxygen bond, and thus the graphene oxide will be reduced to graphene on the substrate. Laser scribing the graphene oxide into graphene allows for very accurate fabrication of graphene designs. An important feature of graphene is the omnidirectional resistance and tunable resistivity [3]. This allows graphene to be considered for applications such as tunable resonators, sensors, tunable absorbers and tunable attenuators. Graphene used in microwave circuits such as tunable attenuators usually focuses on using exfoliated graphene, deposited graphene nanoplatelets, or graphene produced by microwave irradiation. This paper focus on the process of using a laser scribing method to reduce graphene oxide into laser scribed graphene (LSG) used as a voltage variable component to design a prototype tunable LSG microstrip transmission line attenuator over microwave frequencies.