This project will address the need for microwave and millimeter wave signal processing devices which operate in the 10 GHz to 100 GHz range and above using liquid crystal based phase shifters. Current prototype devices show that liquid crystals are promising materials for signal processing over a wide frequency range. Objective 1) Simplification of the current device structures to reduce processing steps. 2) Reduction of losses in liquid crystal devices 3) Identification of liquid crystals with the best performance in the microwave and creation of new liquid crystals materials by doping with high dielectric nanoparticles or ferroelectric nanoparticles. Intellectual Merit The project will result in devices with several important advantages: 1) they will provide a tunable true-time delay or a large tunable phase shift, 2) the devices will require almost no power consumption, 3) there is a low loss tangent over a wide frequency range, 4) the devices will be small and can be integrated into an on-wafer system. Broader Impact The expected commercial and social benefits of the proposed activity will be substantial as the developed devices will have utility in a variety of photonic devices including phase retarders and true time delay lines, micro phased array systems, changeable focus lenses, and beam steering devices. In addition, it will provide new opportunities for the mature liquid crystal industry by creating new non-display applications of liquid crystals. We are planning also for extensive interactions with industry and outreach activities to undergraduate, graduate, and high and middle schools students.
Summary of outcomes This project focused on the development of new platforms for microwave and millimeter wave signal processing devices based on liquid crystals, to address the critical need for microwave and millimeter wave devices which operate in the frequency regime from 10 GHz to 100 GHz and beyond. The research was concentrated on the following main tasks: (a) simplification of the device structures to reduce processing steps (b) reduction of losses in liquid crystal devices, and (c) identification of current liquid crystals with the best performance in the microwave range and creation of new liquid crystal-based materials by doping liquid crystals with high dielectric nanoparticles or ferroelectric nanoparticles. The project attained significant and exciting results. Device-wise, we optimized the device components, such as removal of polyimide layers and its rubbing/annealing steps.Instead, we suggested the use of electrodes themselves as alignment layers for liquid crystal molecules. Only this development simplified the cost and time of production of the devices by twice. Materials-wise, we optimized the liquid crystal performance by adding dielectric and ferroelectric nanoparticles to enhance birefringence and dielectric anisotropy. These nanoparticles are crucial for liquid crystal alignment propagation, which is of tremendous importance in thicker devices. We have found that the addition of such nanoparticles changed dramatically the overall response of the liquid crystal-based device in the microwave and millimeter wave range. The developed device gained attention of two major nation-wide companies interested in production of these devices on a mass scale. The microwave cell (as shown in Fig. 1) resulted in the following benefits: they are inexpensive to produce, on-wafer integration compatible, phase shift over 300°/cm at 110 GHz, continuous broadband operation (from 20 to 100s of GHz), low voltage operation and low power consumption, linear dependence of phase shift vs. frequency, good power handling (at least a few Watts), and electrical tuning speed - up to 1 kHz. (Figure 1: a) Our cell for microwave: middle line length is ~8 mm, thickness of LC is 25 µm. b) Phase shift at different frequencies.) The results have been presented in 5 conferences and published in book chapters and papers. The project has attracted 3 postdoctoral fellows, 2 PhD students and 8 undergraduate students. Furthermore, as recognition of our outstanding education outreach program, the PI (A. Glushchenko) received the University of Colorado Thomas Jefferson Award in 2013.
