# Antenna-on-Chip for Millimeter Wave Applications Using CMOS Process Technology
## 1 Introduction
Recently, antenna-on-chip design has often been considered in area planning and antenna architectures--for example, patch antennas [8,15,17,18,19], numerous meander-line antennas [9], slot antennas [20,21], Yagi-Uda antennas [22], and zig-zag antennas [23]. Among the types of patch antennas, the literature [8] reports a 28 GHz antenna-on-chip for wearable devices, using TSMC 0.18 um CMOS process technology. The antenna size is 1160 um \(\times\) 790 um. The beam steering of the antenna-on-chip is controlled by a parallel coupler design, and the fractional bandwidth is 84.7%. In [15], the patch antenna is proposed and applied in a millimeter wave frequency band for a 5G communication compact front-end receiver and adopts 28 nm CMOS process technology. This structure enhances the radiation gain of the antenna through the PCB-grounded metal structure and reaches 9.8 dBi. In [17], a patch antenna is used to propose an antenna-on-chip with dual frequency bands. The operating frequencies are 77 GHz and 140 GHz, respectively. The frequency bands fall into 63 GHz-78 GHz and 101 GHz-157 GHz. The fractional bandwidth is 21.28% and 35.21%, and the antenna radiation gain is \(-\)3.24 dBi and \(-\)5.795 dBi. The dual-band antenna has more advantages in the application. In [18], monopole patch antennas are designed, as well as specially designed square split ring resonators. By coupling to the feeding antenna, additional resonance is generated to solve the disadvantage of the antenna-on-chip gain drop. The literature experiment adopts 0.13 um SiGe process technology, the working frequency is 81.5 GHz, and it has a gain of 1.61 dBi and a working bandwidth of 77 GHz-87 GHz. In [19], an antenna-on-chip is proposed, which combines a patch antenna with a substrate-integrated waveguide (SIW) and a dielectric resonator antenna (DRA), uses a 65 nm CMOS process with an operating frequency of 94 GHz, and uses an artificial magnetic conductor (AMC) to increase radiation. In [9], a numerous meander-line antenna is proposed, which is applied to the antenna chip in the millimeter wave frequency band. The dual-band operating frequency is 28 GHz and 60 GHz, and it uses 65 nm CMOS process technology. A gain of \(-\)10 dBi and a fractional bandwidth of 5.3% were obtained when measured at 28 GHz. A gain of 0 dBi and a fractional bandwidth of 5.9% were obtained when measured at 60 GHz. This antenna-on-chip has the advantage of dual-band 28 GHz and 60 GHz operation in the millimeter wave frequency band. It is applied in the slot antenna of the antenna-on-chip. In [20], a rectangular ring slot antenna is proposed, using a dielectric resonator antenna (DRA) to make the gain of the antenna-on-chip reach 0 dBi at 40 GHz. In [21], the authors specially designed a back-to-back E-type artificial magnetic conductor (AMC) surface-assisted double-diamond slot structure antenna-on-chip, and it is used in the W-frequency band. It adopts 0.13 \(\upmu\)m CMOS process technology, and the working frequency band is 80-90 GHz. It has a maximum radiation gain of \(-\)0.58 dBi at 84 GHz. The diamond-shaped slot structure antenna array and parasitic elements proposed in this document can obtain a wider bandwidth. In addition, Yagi-Uda antennas are often used as antennas-on-chip. In [22], a solution to the low-gain disadvantage of the antenna-on-chip is proposed, and the Yagi-Uda antenna architecture is designed. Through the basic driving elements, the reflectors and director of the Yagi-Uda antenna and the outer design of the semicircular arc structure increase the radiation gain of the antenna. This design architecture adopts a 180 nm CMOS technology process, the working frequency is 60 GHz, and the radiation gain is \(-\)20 dBi. In [23], the zigzag antenna is designed; the system architecture of the antenna-on-chip is proposed and provides high-speed transmission efficiency. However, the area that can be planned on the top layer of the chip is limited, and how to design an antenna with a high gain and radiation efficiency in the limited area is a big challenge.