Coplanar transitions based on aluminum nitride interposer substrate for terabit transceivers

Abstract

This paper presents two types of coplanar transitions based on aluminum nitride (AlN) substrate for interposer designs of terabit transceivers. The designs of coupled coplanar waveguide (CCPW), coupled line, coplanar waveguide (CPW), and coplanar stripline (CPS) based on AlN substrate are explained. The effects of absorber layer and wire bonding bridges are described. Two types of coplanar transitions are designed and simulated in back-to-back configuration with wire bonding bridges. When driven by differential signal pair, the proposed CCPW-to-coupled line transition in back-to-back configuration with wire bonding bridges achieves a simulated return loss of 11 dB and insertion loss of 2 dB up to 110 GHz. As for single-ended signals, a CPW-to-CPS transition in back-to-back configuration with wire bonding bridges has been designed, fabricated, and measured. The fabricated CPW-to-CPS transition can provide a-3 dB transmission bandwidth up to 80 GHz with associated return loss better than 12 dB.

Ultra-wideband coplanar waveguide-to-asymmetric coplanar stripline transition from DC to 165 GHz

“…In Table 1, this work is compared with other GSG-to-GS transitions published in the literature. Wire bonding bridges are used in [18, 28] for increasing the bandwidth and in order to suppress parasitic modes either thick substrate or absorber layer is needed. Though the transition with air-bridge reported in [29] can achieve a bandwidth of 110 GHz, it requires multilayer patterning process based on thick substrate.…”

“…A CPW-to-CPS transition is reported in [18] with a bandwidth of 55 GHz, the substrate consists of a silicon nitride (Si 3 N 4 ) layer with a thickness of 0.3 µm, a silicon dioxide (SiO 2 ) layer with a thickness of 1 µm, and a silicon (Si) layer with a thickness of 400 µm. As is explained in [28], by placing a PolyOxyMethylene (POM) absorber layer with a thickness of 3.5 mm under an AlN substrate with a thickness of 127 µm, the parasitic modes are eliminated and the bandwidth of the proposed CPW-to-CPS transition increases from 63 GHz to 80 GHz. In [29], a bandwidth of 110 GHz is achieved by the designed CPWto-CPS transition which is based on a GaAs substrate with a thickness of 650 µm.…”

“…By using wire bonding bridges, the proposed CPW-to-CPS transition based on silicon substrate achieves a bandwidth up to 55 GHz. In [28], the designed CPW-to-CPS transition based on aluminum nitride (AlN) substrate with wire bonding bridges can support transmissions from DC to 80 GHz which is used for feeding an indium phosphide (InP) MZM. According to [29], by using reformed air-bridge the demonstrated CPW-to-CPS transition based on gallium arsenide (GaAs) substrate exhibits a bandwidth up to 110 GHz.…”

“…The challenges in designing wideband transitions include characteristic impedance mismatch, mode conversion loss, resonance, and radiation. Several publications can be found for CPW-to-microstrip [24, 25], CPW-to-stripline [26, 27], and CPW-to-CPS [18, 28, 29] transitions while rarely for CPW-to-ACPS transitions. A transition between CPW and CPS used for feeding a multiband dipole antenna was published in [18].…”

Low‐loss broadband (DC to 220 GHz) S‐CPW to S‐CPS transition for S‐CPS coplanar probing

“…The measured back-to-back revealed an insertion loss smaller to 1.1 dB and a return loss higher than 15 dB from 0.5 to 110 GHz. The same concept of air-bridge was utilised in [1,5] but implemented on different processes. Though the mentioned solutions were all fabricated on MMIC process, it is pertinent to address the issue of CPW (or slowwave CPW -S-CPW) to CPS (or S-CPS) transition in the context of CMOS process.…”