Coupling between microstrip lines with finite width ground plane embedded in polyimide layers for 3D-MMICs on Si

Abstract

Abstract--Three-dimenslonal circuits built upon multiple layers of polyimide are required for constructing Si/SiGe monolithic microwave/millimeter-wave integrated circuits on CMOS (low resistivity) Si wafers. Thin film microstrip lines (TFMS) with finite width ground planes embedded in the polyimide are often used. However, the closely spaced TFMS lines are susceptible to high levels of coupling, which degrades circuit performance. In this paper, Finite Difference Time Domain (FDTD) analysis and experimental measurements are used to show that the ground planes must be connected by via holes to reduce coupling in both the forward and backward directions,

Coupling between microstrip lines with finite width ground plane embedded in thin-film circuits

“…In [22], it was experimentally shown that connecting the two ground planes reduces coupling by 5 dB for a 5000 ~lm long coupled line section. FDTD analysis of 3000 J..lm long coup led lines, which is shown in Fig.…”

“…For example, antenna radiation characteristics are modified by changing the ground plane dimensions of microstrip patch antennas [19]- [21]. Coupling between finite width ground plane microstrip lines embedded in polyimide has been experimentally investigated [22]. However, [22] raised questions about parasitic modes that could not be answered experimentally.…”

“…Coupling between finite width ground plane microstrip lines embedded in polyimide has been experimentally investigated [22]. However, [22] raised questions about parasitic modes that could not be answered experimentally. In this paper, an analysis and 25 ~m respectively to yield 50 D. transmission lines for the polyimide thickness, h, of I 0 ~m .…”

“…In this paper, an analysis and 25 ~m respectively to yield 50 D. transmission lines for the polyimide thickness, h, of I 0 ~m . As was proposed in [22] and will be expanded upon here, there is an advantage to connecting the two ground planes. Thus, in several coupled microstrip lines and in the FDTD analysis, the two ground planes on different layers are connected by a single row of 20 ~m by 20 ~m via holes spaced I 00 ~m apart, which is a via spacing less than one hundredth of a wavelength at 25 GHz.…”

A Miniaturized Delay Line based on Slow-Wave Substrates

“…However, the phase shifts provided by these "true" delay lines are proportional to their dimensions which can be a limiting factor when large phase shifts are required. Attempts to squeeze the unit elements of a meander line may result in a size effective device but also enhances the coupling between adjacent elements [5], [6]. Eventually, if the coupling coefficient is large enough, less delay than expected is observed which can cause false switching of active devices or, on a phased array system, radiation towards unwanted direction.…”