Signaling in 3-D integrated circuits, benefits and challenges

Three-dimensional (3-D) or vertical integration is a design and packaging paradigm that can mitigate many of the increasing challenges related to the design of modern integrated systems. 3-D circuits have recently been at the spotlight, since these circuits provide a potent approach to enhance the performance and integrate diverse functions within amulti-plane stack. Clock networks consume a great portion of the power dissipated in a circuit. Therefore, designing a low-power clock network in synchronous circuits is an important task. This requirement is stricter for 3-D circuits due to the increased power densities. Synchronization issues can be more challenging for 3-D circuits since a clock path can spread across several planes with different physical and electrical characteristics. Consequently, designing low power clock networks for 3-D circuits is an important issue. Resonant clock networks are considered efficient low-power alternatives to conventional clock distribution schemes. These networks utilize additional inductive circuits to reduce power while delivering a full swing clock signal to the sink nodes. In this research, a design method to apply resonant clocking to synthesized clock trees is proposed. Manufacturing processes for 3-D circuits include some additional steps as compared to standard CMOS processes which makes 3-D circuits more susceptible to manufacturing defects and lowers the overall yield of the bonded 3-D stack. Testing is another complicated task for 3-D ICs, where pre-bond test is a prerequisite. Pre-bond testability, in turn, presents new challenges to 3-D clock network design primarily due to the incomplete clock distribution networks prior to the bonding of the planes. A design methodology of resonant 3-D clock networks that support wireless pre-bond testing is introduced. To efficiently address this issue, inductive links are exploited to wirelessly transmit the clock signal to the disjoint resonant clock networks. The inductors comprising the LC tanks are used as the receiver circuit for the links, essentially eliminating the need for additional circuits and/or interconnect resources during pre-bond test. Recent FPGAs are quite complex circuits which provide reconfigurablity at the cost of lower performance and higher power consumption as compared to ASIC circuits. Exploiting a large number of programmable switches, routing structures are mainly responsible for performance degradation in FPAGs. Employing 3-D technology can providemore efficient switches which drastically improve the performance and reduce the power consumption of the FPGA. RRAM switches are one of the most promising candidates to improve the FPGA routing architecture thanks to their low on-resistance and non-volatility. Along with the configurable switches, buffers are the other important element of the FPGAs routing structure. Different characteristics of RRAM switches change the properties of signal paths in RRAM-based FPGAs. The on resistance of RRAMswitches is considerably lower than CMOS pass gate switches which results in lower RC delay for RRAM-based routing paths. This different nature in critical path and signal delay in turn affect the need for intermediate buffers. Thus the buffer allocation should be reconsidered. In the last part of this research, the effect of intermediate buffers on signal propagation delay is studied and a modified buffer allocation scheme for RRAM-based FPGA routing path is proposed

Parallel vs. Serial Inter-plane communication using TSVs

3-D integration is a promising prospect for implementing high performance multifunctional systems-on- chip. Through Silicon Vias (TSVs) are the enablers for achieving high bandwidth paths in inter-plane communications. TSVs also provide higher vertical link density and facilitate the heat flow in the 3-D circuits as compared to other potential schemes such as inductive links. However, reliability issues and crosstalk problems among adjacent TSVs decrease the yield and performance of TSV based circuits. Reducing the number of TSVs employed for inter-plane signal transferring can alleviate these problems. This paper proposes to exploit serialization to reduce the number of TSVs in a 3D circuit and presents a comparison between different aspects of TSV-based 3-D circuits such as area, power, crosstalk and yield in parallel and serial vertical links

A Study on Buffer Distribution for RRAM-based FPGA Routing Structures

Compared to Application-Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) provide reconfigurablity at the cost of lower performance and higher power consumption. Exploiting a large number of programmable switches, routing structures are mainly responsible for the performance limitation. Hence, employing more efficient switches can drastically improve the performance and reduce the power consumption of the FPGA. Resistive Random Access Memory (RRAM)-based switches are one of the most promising candidates to improve the FPGA routing architecture thanks to their low on-resistance and non-volatility. The lower RC delay of RRAM-based routing multiplexers, as compared to CMOS-based routing structures encourages us to reconsider the buffer distribution in FPGAs. This paper proposes an approach to reduce the number of buffers in the routing path of RRAM-based FPGAs. Our architectural simulations show that the use of RRAM switches improves the critical path delay by 56% as compared to CMOS switches in standard FPGA circuits at 45-nm technology node while, at the same time, the area and power are reduced, respectively, by 17% and 9%. By adapting the buffering scheme, an extra bonus of 9% for delay reduction, 5% for power reduction and 16% for area reduction can be obtained, as compared to the conventional buffering approach for RRAM-based FPGAs

A Ultra-Low-Power FPGA Based on Monolithically Integrated RRAMs (invited)

Field Programmable Gate Arrays (FPGAs) rely heavily on complex routing architectures. The routing structures use programmable switches and account for a significant share in the total area, delay and power consumption numbers. With the ability of being monolithically integrated with CMOS chips, Resistive Random Access Memories (RRAMs) enable high-performance routing architectures through the replacement of Static Random Access Memory (SRAM)-based programming switches. Exploiting the very low on-resistance state achievable by RRAMs as well as the improved tolerance to power supply reduction, RRAM-based routing multiplexers can be used to significantly reduce the power consumption of FPGA systems with no performance compromises. By evaluating the opportunities of ultra-low-power RRAM-based FPGAs at the system level, we see an improvement of 12%, 26% and 81% in area, delay and power consumption at a mature technology node

Low Power FPGAs Based on Resistive Memories

During the last three decades, reconfigurable logic has been growing steadily and can now be found in many different fields. Field programmable gate arrays (FPGAs) are one of the most famous architecture families of reconfigurable devices. FPGAs can be seen as arrays of logic units that can be reconfigured to realize any digital systems. Their high versatility has enabled designers to drastically reduce time to market, and made FPGAs suitable for prototyping or small production series in many branches of industrial products. In addition, and thanks to innovations at the architecture level, FPGAs are now conquering segments of mass markets such as mobile communications. Reconfigurable Logic: Architecture, Tools, and Applications offers a snapshot of the state of the art of reconfigurable logic systems. Covering a broad range of architectures, tools, and applications, this book: Explores classical FPGA architectures and their supporting tools Evaluates recent proposals related to FPGA architectures, including the use of network-on-chips (NoCs) Examines reconfigurable processors that merge concepts borrowed from the reconfigurable domain into processor design Exploits FPGAs for high-performance systems, efficient error correction codes, and high-bandwidth network routers with built-in security Expounds on emerging technologies to enhance FPGA architectures, improve routing structures, and create non-volatile configuration flip-flops Reconfigurable Logic: Architecture, Tools, and Applications reviews current trends in reconfigurable platforms, providing valuable insight into the future potential of reconfigurable systems.</p