Modeling and Design Techniques for 3-D ICs under Process, Voltage, and Temperature Variations

Three-dimensional (3-D) integration is a promising solution to further enhance the density and performance of modern integrated circuits (ICs). In 3-D ICs, multiple dies (tiers or planes) are vertically stacked. These dies can be designed and fabricated separately. In addition, these dies can be fabricated in different technologies. The effect of different sources of variations on 3-D circuits, consequently, differ from 2-D ICs. As technology scales, these variations significantly affect the performance of circuits. Therefore, it is increasingly important to accurately and efficiently model different sources of variations in 3-D ICs. The process, voltage, and temperature variations in 3-D ICs are investigated in this dissertation. Related modeling and design techniques are proposed to design a robust 3-D IC. Process variations in 3-D ICs are first analyzed. The effect of process variations on synchronization and 3-D clock distribution networks, is carefully studied. A novel statistical model is proposed to describe the timing variation in 3-D clock distribution networks caused by process variations. Based on this model, different topologies of 3-D clock distribution networks are compared in terms of skew variation. A set of guidelines is proposed to design 3-D clock distribution networks with low clock uncertainty. Voltage variations are described by power supply noise. Power supply noise in 3-D ICs is investigated considering different characteristics of potential 3-D power grids in this thesis. A new algorithm is developed to fast analyze the steady-state IR-drop in 3-D power grids. The first droop of power supply noise, also called resonant supply noise, is usually the deepest voltage drop in power distribution networks. The effect of resonant supply noise on 3-D clock distribution networks is investigated. The combined effect of process variations and power supply noise is modeled by skitter consisting of both skew and jitter. A novel statistical model of skitter is proposed. Based on this proposed model and simulation results, a set of guidelines has been proposed to mitigate the negative effect of process and voltage variations on 3-D clock distribution networks. Thermal issues in 3-D ICs are considered by carefully modeling thermal through silicon vias (TTSVs) in this dissertation. TTSVs are vertical vias which do not carry signals, dedicated to facilitate the propagation of heat to reduce the temperature of 3-D ICs. Two analytic models are proposed to describe the heat transfer in 3-D circuits related to TTSVs herein, providing proper closed-form expressions for the thermal resistance of the TTSVs. The effect of different physical and geometric parameters of TTSVs on the temperature of 3-D ICs is analyzed. The proposed models can be used to fast and accurately estimate the temperature to avoid the overuse of TTSVs occupying a large portion of area. A set of models and design techniques is proposed in this dissertation to describe and mitigate the deleterious effects of process, voltage, and temperature variations in 3-D ICs. Due to the continuous shrink in the feature size of transistors, the large number of devices within one circuit, and the high operating frequency, the effect of these variations on the performance of 3-D ICs becomes increasingly significant. Accurately and efficiently estimating and controlling these variations are, consequently, critical tasks for the design of 3-D ICs.

Effects of Process Variations on 3-D Global Clock Distribution Networks

Giovanni De Micheli, Vasileios Pavlidis, Hu Xu

In three-dimensional (3D) integrated circuits, the effect of process variations on clock skew differs from 2D circuits. The combined effect of inter-die and intra-die process variations on the design of 3D clock distribution networks is considered in this article. A statistical clock skew model incorporating both the systematic and random components of process variations is employed to describe this effect. Two regular 3D clock tree topologies are investigated and compared in terms of clock skew variation. The statistical skew model used to describe clock skew variations is verified through Monte-Carlo simulations. The clock skew is shown to change in different ways with the number of planes forming the 3D IC and the clock network architecture. Simulations based on a 45-nm CMOS technology show that the maximum standard deviation of clock skew can vary from 15 ps to 77 ps. Results indicate that simply increasing the number of planes of a 3D IC does not necessarily lead to lower skew variation and higher operating frequencies. A multigroup 3D clock tree topology is proposed to effectively mitigate the variability of clock skew. Tradeoffs between the investigated 3D clock distribution networks and the number of planes comprising a 3D circuit are discussed and related design guidelines are offered. The skew variation in 3D clock trees is also compared with the skew variation of clock grids.

Assoc Computing Machinery2012

Heat Management for Process Intensification of Fast Exothermic Reactions in Microstructured Reactors

Julien Haber

Nowadays, the production in fine chemical and pharmaceutical industry is mostly carried out in large scale batch reactors having typically dimensions of a few meters to satisfy the demand of the market. Even though this technology has been widely used and developed for centuries, it is by far not optimal for every type of reaction. For example, when working with exothermic reactions, the produced heat can’t be always fully evacuated. To avoid run-aways, high amounts of solvents are used to increase the heat capacity of the mixture, or semi-batch mode with a slow addition of one of the reactants. In both cases, the space-time yield, i.e. mass of product produced per unit of time and per unit of volume, drastically diminishes. One of the main enabling technologies allowing process intensification are the microstructured devices, characterized by high heat and mass transport rates due to the small characteristic dimensions (< 1mm). Using this type of equipment, almost isothermal conditions can be achieved while carrying out fast exothermic reactions (with characteristic reaction times down to tr ≈ 10 s). Thereby, the target throughput is reached by numbering-up, i.e. parallel connection of several identical microreactors. For very fast exothermic reactions, especially for quasi-instantaneous reactions, dimensions smaller than 100 μm are needed to prevent the formation of unwanted hot spots. As such small dimensions are not suitable for industrial scale due to possible clogging and high pressure drops, other solutions are warranted. The aim of this thesis is to develop alternative microstructured reactors enabling quasi-instantaneous reactions to be carried out under intensified conditions while suppressing the large hot spots. The work is divided into two main parts: determination of suitable strategies for the microstructured reactor design via numerical simulations (Chapter 3) and the experimental validation of the best microstructured reactor concept (Chapter 4-6). Three strategies for enhanced temperature control within microstructured reactors for quasi-instantaneous reactions are taken for analysis using numerical simulation: 1) reduction of hot spot temperature by increased axial heat transfer in the reactor wall, 2) by injection of one reactant in multiple points along the reactor length and 3) by continuous injection of one reactant through a porous wall in a concentric reactor geometry. The multi-injection reactor (option 2) is the most effective design since with an optimized dosing with only 4 injection points the temperature rise is 5-fold smaller as compared to the adiabatic temperature rise. Furthermore, the key design requirements for an efficient multi-injection reactor are identified: 1) complete mixing after each injection and 2) evacuation of the produced heat before reaching the next injection point. To experimentally validate the simulation results, in the subsequent chapter, an experimental method to monitor temperature in microstructured reactors is developed (Chapter 4). To track axial temperature profiles quantitatively, a method based on non-intrusive infrared thermography is developed yielding a resolution of 100 points/mm2 and a precision of 1 °C. In the first validation experiments, the heat transfer coefficient determined in a micro heat exchanger (574 W/m2K) is in good agreement with prior estimations. While carrying out the hydrolysis of tetraethoxysilane as a fast model reaction, incomplete mixing of the reactants is detected via the temperature profile, and is ascribed to the high difference in density of the inlet flows. Applying the method of quantitative IR-thermography to a T-micromixer with circular cross section gives insight into the mixing phenomenon (Chapter 5). The latter is studied via the temperature profile of the reactions strongly controlled by mixing, i.e. dilution of sulfuric acid with water and cyclization of pseudoionone. The mass transfer coefficients determined are in the order of 0.1-9 1/s. It is shown that at high Fourier numbers Fo = tdiff/τ (mixing by shearing), the Damköhler number DaI= τ/tmix remains constant with respect to flow rate at the reactor outlet, as both, mixing time and residence time decrease proportionally with the latter parameter. To enhance the mixing performance, two approaches are applied: 1) the introduction of a carrier phase leading to travelling micro-batches with up to 4-fold faster mixing and 2) the structuring of the channel walls leading to the formation of vortices, and thus, to a substantially improved mixing efficiency. For efficient mixing in the multi-injection reactor (Chapter 6), two types of mixing structures, i.e. the tangential mixer and the herringbone mixer, are developed using low temperature co-fired ceramics, and compared using quantitative infrared thermography. The best mixing performance is obtained by the herringbone structure, providing efficient mixing in a large range of flow rates corresponding to Reynolds numbers Re = 20-130. Finally, a multi-injection reactor comprising three injection points and the herringbone microstructure is developed. Using the quasi-instantaneous and exothermic cyclisation of pseudoionone to α-ionone and β-ionone as model reaction, it is demonstrated that the temperature rise can be reduced 8-fold compared to the adiabatic temperature rise due to 1) the high volumetric heat transfer coefficient in the order of 4·106 W/(m3K), 2) the reduced overall transformation rate due to gradual mixing within the herringbone structure and 3) the injection of pseudoionone at three injection points. Yields of α-ionone and β-ionone above 98 % are achieved at a residence time of 3.7 s while efficiently avoiding the unwanted consecutive polymerization in a temperature range of 30-60 °C. Compared to the conventional semi-batch process, where such high yields can only be attained at temperatures below 10 °C, a 500-fold increased space-time- yield is achieved. In addition to the intensification of the process, the required mass of solvent is halved while maintaining good temperature control, rendering the overall process safe.

EPFL2013

Analysis, modeling and design of a CMOS Super-Regenerative Receiver for implanted medical devices under square and sinusoidal quench signals

Catherine Dehollain, Naci Pekçokgüler

Medical implant devices have found widespread application in recent years. The Super-Regenerative Receiver has been one preferred architecture due to its power advantage over other architectures. We present a detailed analysis of the circuits and their equivalent models to be used in system level design of a Super-Regenerative Receiver in this paper. The design procedure is also demonstrated with a receiver design example. Designs were carried out in UMC 180 nm process with a center frequency of 416 MHz for MedRadio band. Errors between the simulation results of the proposed model and actual circuits are less than 1.6% for LNA characteristics and 7% for receiver output amplitude. 10 Mbps data rate was achieved with 432 pJ/bit energy consumption over 1.8 V power supply. The study is concluded with the simulation results of the circuits and the equivalent models.

ELSEVIER SCIENCE BV2019

Heat Management for Process Intensification of Fast Exothermic Reactions in Microstructured Reactors

Julien Haber

EPFL2013