Millimeter Wave On-chip Antennas and Metamaterial in Silicon
- Author(s): Pan, Shiji
- Advisor(s): Capolino, Filippo
- et al.
Aggressive scaling of (Bi)CMOS technology has enabled the designs of highly integrated transmitting and receiving system in silicon at millimeter waves (mm-waves). At mm-wave frequencies, when the antenna's form factor is in the order of several millimeters, the integration of antenna on the silicon chip is becoming feasible. The idea of on-chip antenna (OCA) has triggered considerable interest, as it allows the ultimate on-die integration of the entire wireless transceiver, eliminating the need for any off-chip interconnection. However, designing a high gain and high efficiency OCA is very challenging because of the high permittivity and low resistivity of the silicon or SiGe substrate. An OCA with silicon substrate will lose much of its power inside the silicon, thereby resulting in low radiation efficiency, low gain and possible electromagnetic interference with the active circuitry. To avoid that, a shielding ground plane above the silicon is desired and in that way the insulator layer acts as the antenna substrate. However, because of the extremely thin thickness of insulator layer (around 5 &mum to 20 &mum) the antenna bandwidth is extremely narrow and the radiation efficiency is very low in general.
This work explores the ideas of using metamaterial surfaces (metasurfaces) in OCA design. The metasurface is used for OCA design in two different configurations: one is as a reflector below the OCA and the other is as an antenna directly. It is found that under the CMOS environment, the artificial magnetic conductor (AMC) property of metasurface as a reflector cannot be guaranteed at the resonance when the thickness of the metasurface becomes very thin. Based on an equivalent model, the threshold condition of AMC appearance and the AMC bandwidth formula is derived. Meanwhile, the design of using metasurface as a leaky wave antenna (LWA) was implemented at 94 GHz in a 0.18 &mum BiCMOS. The results show the widest relative impedance bandwidth and are among the highest gain ever achieved for OCA considering an extremely thin substrate thickness, as confirmed by both simulations and measurements. A similar antenna operating at 0.31 THz was fabricated in a 65 nm CMOS technology and the simulation results are shown in this work.
Several novel OCA designs are also presented, including a rectangular cavity backed slot antenna, a substrate integrated waveguide (SIW) slot antenna and an E-shaped patch antenna. Even though these antennas have extremely thin substrates, these designs show improved impedance bandwidth and gain compared to the previous designs in the literature. For the sake of wideband operation, an on-chip bowtie shaped slot antenna is implemented both as a single element and in a phased array configuration in a 0.18 &mum BiCMOS technology.
Additional research into the potential for applying metamaterial in CMOS devices is also explored. The novel concept for applying split ring resonator in on-chip slow wave transmission line (SWTL) design in silicon is presented.