Electrical caracterization, modeling and optimization in RF & mmW of devices on 3DSI technology

Published : 15 July 2019

3D sequential integration (3DSI) is currently showing an industrial appeal for More Moore and More than Moore applications. It is an alternative to the traditional scaling for computing application. It increases the density, efficiency and performance of digital chips without reducing the transistor size. 3DSI opens the possibility to novel configurations such us analog-digital and analog-analog. RF applications is one potential field. Current existing solutions such as FEM technologies (PDSOI, GaN) and Silicon photonics are still limited because of interconnections. 3DSI offers higher transistor density, small parasitic and interconnect length reduction, which should lead to better performance for millimeter-wave (mmW) circuits. Thanks to 3DSI performant digital tier close to the RF.

RF first measurements will be performed in 2018 on existing Coolcube devices in order to characterize small-signal transistor parameters from each level. It will provide useful characterization data for device optimization (RC network extraction). During the thesis, the candidate will characterize different variants of process integrations assessed for 3DSI (junctionless, full planar transistor…). Moreover, additional specific analog/RF designs will be layouted in the next coolcube tape-out (September 2019), whose silicon is expected for 2020. Planar FDSOI reference will be also designed and characterized as reference. It will enable a benchmark of technologies.

The goal of the PhD is to evaluate 3DSI potential for mmW. The candidate will have access to state-of-the-art electrical characterization setups, allowing high frequency measurement capability. In the first place, the candidate will study each 3DSI level performances in mmW, then the interconnections between tiers and later the effect between tiers. The candidate will propose specific tests structures (Transmission , filter, LNA..) to fully measure technology characteristics at mmW, together with more complex analog+digital characterization in order to evaluate their performance in an application-like environment (crossover, endurance ageing, heating…). The output of the RF characterization will feed the FDSOI and 3DSI SPICE models, currently under development.

The thesis will be in interaction with process and design team. Together with advanced electrical characterization, the PhD candidate will feedback to improve process conditions, design rules and electrical performance. He/she will propose the optimal stack and technology (ground planes, intermediate metal lines, transistor…) in order to reach the best tradeoff for both analog and digital performances. The candidate will propose different ways for further device optimization, either based on updated process conditions or electromagnetic simulations.

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