Nematic Liquid Crystal Composite Materials for DC and RF Switching

Project by Mohiuddin Munna

Liquid Crystals (LC) are widely used in displays, electro-optic modulators, and optical switches. In these types of devices, an electric field is applied which modulates the optical properties of the LC material. It is attractive for its low power consumptions. Opto-electronic devices and switches made from LC materials consume comparatively less power than opto-mechanical counterparts and other electronic display technologies. There are only a few works done on all electrical switches and sensors. In this research, our goal is to design, simulate and fabricate LC switching devices and test the capacitive and resistive responses under DC and low-frequency AC and RF loads, using various electrode configurations. We will study electrode configurations that result in high sensitivity, low response time, and high on/off ratio. We have already done simulation and design using a simple analytic model, and a lithography mask. Our simulations and RF analysis suggest that RF switching with acceptable performance may be possible. LC materials in DC and RF switching application may open a new avenue for a low-cost solution.

MEMS based Gas Sensing

Project by Turja Nandy

In this project, we will introduce MEMS membrane-based photo-acoustic (PA) detection system for a hazardous gas sensing application with high accuracy and low cost. We will use thin and deformable micro-machined SOI membrane to detect the acoustic vibration created via light-gas interaction inside the PA chamber. In this work, firstly, we will analyze the theory behind photo-acoustic phenomena and pressure change inside gas chambers for proper modeling of a MEMS membrane. Then, we will fabricate the MEMS membrane and prepare the whole optical experimental set-up with a LED-based infrared (IR) light source and detector according to the absorption spectra of target gases. Finally, we will detect the membrane deflection caused by acoustic vibrations and pressure change through a white light interferometer. These deflection values will give the sensitivity towards the particular gas.

Figure 1 3D printed photo-acoustic chamber model .

Figure 2 Bottom view of MEMS SOI membrane

Microcontact Novel Test Fixture for Reliability and Performance Study

Project by Protap Mahanta

Microelectromechanical systems (MEMS) technology is widely used in applications ranging from sensing to switching technology due to its low cost, low power consumption, and small geometries. Microswitches are an example of a MEMS technology that shows promising performances in direct current (DC) and radio frequency (RF) applications. However, reliability is of great concern for them to be ubiquitously used by the industry where the lifetime requirement is typically 1-10 billion cycles depending on the specific application. Microcontact surface tribology plays a crucial role in determining reliability and performance. A test fixture facilitates to study contact force, contact resistance, adhesion, and contamination associated with the microcontact. Currently, we are developing an improved microcontact support structure which enables a simple, quick, and easy post-mortem contact surface analysis. In addition, engineered micro-electrical contacts will be fabricated and tested using our novel test fixture for acquiring significant data to design a robust and reliable MEMS switch for future DC and RF applications.

Figure 1. Schematic representation of the microcontact test fixture assembly.

Thin Films

Gallium nitride (GaN), a wide bandgap semiconductor, has few superior material properties such as: a large electric breakdown field, high electron velocity, and mobility, which makes it a potential candidate for next generation electrical and optoelectrical applications. At present, most of the GaN growth is done on relatively expensive substrates i.e. sapphire and SiC by using high-temperature deposition methods (MBE, MOCVD etc). On the other hand, Silicon substrates are cheap, available in large diameters and have well characterized electrical and thermal properties. Despite all these advantages, GaN on Si is not studied much because of the cracking problem in GaN films which becomes worse at a higher temperature. Therefore, our focus is to grow the good quality and less stressed GaN films on Si, using the low-temperature atomic layer deposition (ALD) method. In the future, our plan is to design and fabricate GaN/Si devices and study their reliability, performance for industrial applications.

Cost Effective Membranes

We are currently designing a low-cost water pressure sensor chip. The main functions of these chips are seen in every day utilities, in every day water utilities and applications such as automated water fixtures, washing machines, etc. Our goal is to create cost effective, multiple application devices using advanced materials and properties such as piezoelectric and piezoresistivity.