B. Parvais

3D stacked IC demonstration using a through Silicon Via First approach

We report for the first time the demonstration of 3D integrated circuits obtained by die-to-die stacking using Cu Through Silicon Vias (TSV). The Cu TSV process is inserted between contact and M1 of our reference 0.13 mum CMOS process on 200 mm wafers. The top die is thinned down to 25 mum and bonded to the landing wafer by Cu-Cu thermo-compression. Both top and landing wafers contain CMOS finished at M2 to evaluate the process impact both FEOL and BEOL. The results confirm no degradation of the FEOL performance. The functionality of various ring oscillator topologies that include inverters distributed over both top and bottom dies connected through TSVs demonstrates excellent chip integrity after the TSV and 3D stacking process.

Ultra low-EOT (5 Å) gate-first and gate-last high performance CMOS achieved by gate-electrode optimization

A novel gate first integration approach enabling ultra low-EOT is demonstrated. HfO₂ based devices with a zero interface layer and optimized gate-electrode is used to achieve EOT and T_inv values of ˜5 Å and ˜8 Å respectively for both n and pMOS devices. The drive currents at I_off=100 nA/μm with V_DD=1 V is 1.4 mA/μm and 0.6 mA/μm (no SiGe source/drain) for n and pMOS respectively. The technology further offers low n/pMOS V_T of 0.3/-0.4V, good V_T-uniformity, and V_T-matching and very high cutoff frequencies at ˜290-340 GHz for 38 nm nMOS devices. A replacement poly gate process is used to further improve upon the pMOS effective work function. TDDB lifetimes over 10 years are reported while BTI indicates potential reliability challenges.

Planar Bulk MOSFET s Versus FinFETs: An Analog/RF Perspective

Comparison of digital and analog figures-of-merit of FinFETs and planar bulk MOSFETs reveals an interesting tradeoff in the analog/RF design space. It is found that FinFETs possess the following key advantages over bulk MOSFETs: reduced leakage, excellent subthreshold slope, and better voltage gain without degradation of noise or linearity. This makes them attractive for digital and low-frequency RF applications around 5 GHz, where the performance-power tradeoff is important. On the other hand, in high-frequency applications, planar bulk MOSFETs are seen to hold the advantage over FinFETs due to their higher peak transconductance. However, this comes at a cost of a reduced voltage gain of bulk MOSFETs

Device and circuit-level analog performance trade-offs: a comparative study of planar bulk FETs versus FinFETs

Comparison of digital and analog figures-of-merit of FinFETs and planar bulk MOSFETs reveals an interesting trade-off in analog/RF design space. It is seen that FinFETs possess key advantages over bulk FETs for applications around 5 GHz where the performance-power trade-off is important. In case of higher frequency applications bulk MOSFETs are shown to hold the advantage on account of their higher transconductance (Gm), provided a degraded voltage gain and a higher leakage current can be tolerated

A low-power radio chipset in 40nm LP CMOS with beamforming for 60GHz high-data-rate wireless communication

The link budget of multi-Gb/s wireless communication systems around 60GHz improves by beamforming. CMOS realizations for this type of communication are mostly limited to either one-antenna systems [1], or beamforming ICs that do not implement all radio functions [2]. The sliding-IF architecture of [3] uses RF phase shifting, which deteriorates noise performance.

Identifying the Bottlenecks to the RF Performance of FinFETs

In this work, the high frequency (RF) performance of FinFETs is investigated in detail using a two-level parasitic model comprising outer and inner parasitic capacitances in addition to parasitic series resistances. Use of scaling relations of these parasitic capacitances with numbers of fins and fingers allows extraction of these elements. Next, by defining a series of reference surfaces, each associated with a certain set of parasitic elements, we proceed to calculate the RF Figures of Merit, namely fT and fmax at these surfaces. These are called ‘available fT (fmax)’ in this work. Analysis of the available fT (fmax) gives insight into the extent to which different parasitics affect the FinFET’s RF performance. The main bottleneck to the FinFET’s RF performance is identified, solutions are proposed and relevant trade-offs are discussed.

Migrating from planar to FinFET for further CMOS scaling: SOI or bulk?

The multi-gate architecture is considered as a key enabler for further CMOS scaling. FinFETs can readily be manufactured on SOI or bulk substrates. We report for the first time an extensive benchmark of their critical electrical figures of merit. Both alternatives show better scalability than PLANAR CMOS and exhibit similar intrinsic device performance. Introducing SOI substrates and low doped fins results in lower junction capacitance, higher mobility and voltage gain with reduced mismatch. Using an optimized integration to minimize parasitics we demonstrate high-performing FinFET ring-oscillators with delays down to 10ps/stage for both SOI and bulk FinFETs and working SRAM cells at VDD=1.0V.

The device architecture dilemma for CMOS technologies: Opportunities & challenges of finFET over planar MOSFET

Despite their excellent control of short channel effects, FinFETs suffer from different trade-offs in the mixed-signal domain, with respect to planar devices. For the first time, we report a complete and comprehensive comparative analysis showing that these trade-offs can be alleviated in advanced FinFET technology. As such, higher voltage gain and transconductance than planar MOSFETs are reached at the same time. VT mismatch smaller than 3mV.µm is obtained for narrow (10nm) fins. Reduced speed sensitivity to gate pitch scaling and invertor delay reduced below 10 ps will be demonstrated.

Design of Ultra-Wideband Low-Noise Amplifiers in 45-nm CMOS Technology: Comparison Between Planar Bulk and SOI FinFET Devices

This paper deals with the design of single-stage differential low-noise amplifiers for ultra-wideband (UWB) applications, comparing state-of-the-art planar bulk and silicon-on-insulator (SOI) FinFET CMOS technologies featuring 45-nm gate length. To ensure a broadband input impedance matching, the g m-boosted topology has been chosen. Furthermore, the amplifiers have been designed to work over the whole UWB band (3.1-10.6 GHz), while driving a capacitive load, which is a realistic assumption for direct conversion receivers where the amplifier directly drives a mixer. The simulations (based on compact models obtained from preliminary measurements) highlight that, at the present stage of the technology development, the planar version of the circuit appears to outperform the FinFET one. The main reason is the superior cutoff frequency of planar devices in the inversion region, which allows the achievement of noise figure and voltage gain comparable to the FinFET counterpart, with a smaller power consumption.

Suitability of FinFET technology for low-power mixed-signal applications

Wireless applications require a low power technology that enables digital/analog/RF functions on the same chip. FinFET technology presents a competitive alternative to planar CMOS as it features good digital, analog and low-frequency noise performances. Also, very good matching performance is presented here for the first time. Moreover, FinFETs are shown to be attractive for low-power applications below 10 GHz. The suitability of Fin varactors is evaluated and tradeoffs are given. An inductorless oscillator with large tuning range (1-8.5 GHz) for low-power wideband applications is demonstrated for the first time