Ferroelectric beam‐steering antenna

Abstract

A miniaturised antenna array on a ferroelectric substrate with extraordinary beam-steering capabilities at low applied voltages has been developed by researchers in Romania and Ireland. Phased antenna arrays have a radiation pattern that is the combination of the electromagnetic emissions from individual array elements in different excitation phases. This technology is largely exploited in radar and communication systems due to its electronic beam-steering capabilities. When this technology is integrated into low-power wireless applications or integrated circuits, the phase shifters require low applied voltages to allow reconfiguration of the radiation patterns. In this respect, there is a need for low-voltage controlled phased antenna arrays to be commercialised on a large-scale for 5G communications. RF/biasing measurement setup of the HfZrO-based phased antenna array that was characterised at IMT Detail of the bias circuit for the phase shifters in the HfZrO-based phased antenna array When designing miniaturised antenna arrays for low power wireless communication devices, several issues need to be considered. These include the fact that planar antennas need to be deposited onto very thin substrates with medium/high permittivity values to reduce the device dimensions, and a high radiation efficiency/gain must be achieved by the final device. HfZrO-based ferroelectrics have demonstrated outstanding capabilities for these low power devices as they have high CMOS compatibility, thin deposited layers (5–10 nm), good stability with time and under mechanical/thermal stress and functional ferroelectric properties at low applied voltages. In this Issue of Electronics Letters, Martino Aldrigo and colleagues from IMT Bucharest and Tyndall National Institute, University College Cork, present the full experimental characterisation of a miniaturised antenna phased array that operates in the S frequency band and is suitable for low-power wireless devices. The phase array consists of two gold patch antennas, phase shifters and additional circuitry; all integrated on a wafer of HfxZr1−xO2/high-resistivity silicon. The radiation beam at 2.55 GHz is steered 25° when the 7 nm-thick ferroelectric is biased at low applied DC voltages. This result was obtained while preserving a good gain value (5.36 dBi), in spite of the losses introduced by the ferroelectric material, with an extraordinary figure of merit; FOM = 26.88°/V at 2.55 GHz. Several major challenges had to be overcome in this work, including optimising the growth of HfZrO ferroelectric material, designing a two-element patch antenna array to fit into a four inch HR Si wafer, designing two autonomously-biased phase shifters for the two antennas and optimising the measurement setup to characterise the phased array. The authors believe this work introduces the first prototype of a compact, CMOS-compatible phased antenna array with integrated phase shifters on a ferroelectric HfZrO thin film that offers interesting beam-steering capabilities at low applied voltages. “This is an unprecedented result in the domain of ferroelectric-based microwave devices”. “This work will arouse a growing interest in ferroelectric materials for microwave applications, in view of the increasing demand of performing low-voltage (and low-cost) electronics for 5G-based IoT devices” states Aldrigo. The most important longer-term developments may come from enhancements of the ferroelectric-based phase shifters and from new antenna layouts. Since reporting the work in their Letter, Aldrigo and colleagues have been working on new layouts of ferroelectric-based phase shifters in order to embed them with different antenna layouts. Aldrigo explains “we hope to achieve better performance at even higher frequencies. In this respect, it is our firm intention to further develop the work reported in our Letter.” There are a few major limitations and unexplored avenues associated with this work and research field in general according to the IMT/Tyndall team. New compositions of novel ferroelectric materials could be explored and the thickness of ferroelectric material that guarantees the best magnetic and electronic properties could be further optimised. Additionally, phase shifter layouts that offer the largest phase shift (at the desired frequency) with low insertion loss (i.e. less than 2 dB) and at low bias voltages could also be investigated. Finally, the “smart” integration of ferroelectric-based phase shifters in phased antenna arrays with steering capabilities of ± 90° remains a goal in this research field.