IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

This paper describes the design and implementation of an 80-kb logic-embedded non-volatile multi-time programmable memory (MTPM) with no added process complexity. Charge trap transistors (CTTs) that exploit charge trapping and de-trapping behavior in high-K dielectric of 32-/22-nm Logic FETs are used as storage elements with logic-compatible programming voltages. A high-gain slew-sense amplifier (SA) is used to efficiently detect the threshold voltage difference (Δ VDIF) between the true and complement FETs in the twin cell. Design-assist techniques including multi-step programming with over-write protection and block write algorithm are used to enhance the programming efficiency without causing a dielectric breakdown. High-temperature stress results show a projected data retention of 10 years at 125 °C with a signal loss of &lt;30% that is margined in while programming, by employing a sense margining logic in the SA. Scalability of CTT has been established by the first demonstration of CTT-based MTPM in 14-nm bulk FinFET technology with read cycle time of 40 ns at 0.7-V VDD. © 1966-2012 IEEE.

Department of Electrical Engineering

IEEE Journal of Solid-State Circuits

80-kb Logic Embedded High-K Charge Trap Transistor-Based Multi-Time-Programmable Memory with No Added Process Complexity

A 1.1 Mb embedded DRAM macro (eDRAM), for next-generation IBM SOI processors, employs 14 nm FinFET logic technology with 0.0174 m deep-trench capacitor cell. A Gated-feedback sense amplifier enables a high voltage gain of a power-gated inverter at mid-level input voltage, while supporting 66 cells per local bit-line. A dynamic-AND-gate-thin-oxide word-line driver that tracks standard logic process variation improves the eDRAM array performance with reduced area. The 1.1 Mb macro composed of 8×2 72 Kb subarrays is organized with a center interface block architecture, allowing 1 ns access latency and 1 ns bank interleaving operation using two banks, each having 2 ns random access cycle. 5 GHz operation has been demonstrated in a system prototype, which includes 6 instances of 1.1 Mb eDRAM macros, integrated with an array-built-in-self-test engine, phase-locked loop (PLL), and word-line high and word-line low voltage generators. The advantage of the 14 nm FinFET array over the 22 nm array was confirmed using direct tester control of the 1.1 Mb eDRAM macros integrated in 16 Mb inline monitor. © 2015 IEEE.

World University root node

Department of Management Studies

A 14 nm 1.1 Mb embedded DRAM macro with 1 ns access

An 80Kb logic Embedded Multi-Time Programmable Memory (MTPM) employs charge trapping and de-trapping behavior in 32nm/22nm High-K transistor, resulting in no added process complexity. Multi-step verification with overwrite protection employs block-write and signal margin degradation (∼30%) to satisfy 10 year retention at 105° C. © 2016 IEEE.

Department Of Biotechnology

Department of Mathematics

IEEE Symposium on VLSI Circuits, Digest of Technical Papers

80Kb 10ns read cycle logic Embedded High-K charge trap Multi-Time-Programmable Memory scalable to 14nm FIN with no added process complexity

A technique for extracting statistical compact model parameters using artificial neural networks (ANNs) is proposed. ANNs can model a much higher degree of nonlinearity compared to existing quadratic polynomial models and, hence, can even be used in sub-100-nm technologies to model leakage current that exponentially depends on process parameters. Existing techniques cannot be extended to handle such exponential functions. Additionally, ANNs can handle multiple input multiple output relations very effectively. The concept applied to CMOS devices improves the efficiency and accuracy of model extraction. Results from the ANN match the ones obtained from SPICE simulators within 1%. © 1982-2012 IEEE.

IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems

Statistical compact model extraction: A neural network approach

Artificial neural networks (ANNs) have shown great promise in modeling circuit parameters for computer aided design applications. Leakage currents, which depend on process parameters, supply voltage and temperature can be modeled accurately with ANNs. However, the complex nature of the ANN model, with the standard sigmoidal activation functions, does not allow analytical expressions for its mean and variance. We propose the use of a new activation function that allows us to derive an analytical expression for the mean and a semi-analytical expression for the variance of the ANN-based leakage model. To the best of our knowledge this is the first result in this direction. Our neural network model also includes the voltage and temperature as input parameters, thereby enabling voltage and temperature aware statistical leakage analysis (SLA). All existing SLA frameworks are closely tied to the exponential polynomial leakage model and hence fail to work with sophisticated ANN models. In this paper, we also set up an SLA framework that can efficiently work with these ANN models. Results show that the cumulative distribution function of leakage current of ISCAS'85 circuits can be predicted accurately with the error in mean and standard deviation, compared to Monte Carlo-based simulations, being less than 1% and 2% respectively across a range of voltage and temperature values. © 2006 IEEE.

Voltage and temperature aware statistical leakage analysis framework using artificial neural networks

We propose a logic gate leakage model based on transistor stacks, which includes local transistor level process variation parameters along with global process variation parameters and supply and temperature. The stack models include both subthreshold as well as gate leakage and consider the input vector state. We examine cells from an industrial standard cell library and find that most cells can be modeled with simple stacks, which have a linear chain of transistors. However some gates like XOR, Majority or Muxes need complex stacks and we show how these can be modeled. Our experiments show that only 18 different stack models are needed to predict the leakage of all gates in this industrial library. Re-use of the same models for pass transistor logic circuits and multi-finger transistors is also demonstrated. We explicitly include voltage and temperature into the models to support joint estimation of power supply IR drops and leakage currents, as well as enable analysis for dynamic voltage scaling applications. We use artificial neural networks to create unified models which include global and local process variations, supply voltage in the range of VDD/2 – VDD and temperature in the range 0–100 °C. These models are very useful for performing statistical leakage analysis of large circuits. Results from the ISCAS'85 benchmark circuits show that neural network based stack models can predict the PDF of leakage current of large circuits across supply voltage and temperature accurately with the average error in mean being less than 2% and that in standard deviation being less than 7% when compared to SPICE. Further gate level validation has been done for both an industrial 130 nm and 45 nm PTM model files.

Journal of Low Power Electronics

Voltage and Temperature Scalable Logic Cell Leakage Models Considering Local Variations Based on Transistor Stacks

With extensive use of Dynamic Voltage Scaling (DVS) there is increasing need for voltage scalable models. Similarly, leakage being very sensitive to temperature motivates the need for a temperature scalable model as well. We characterize standard cell libraries for statistical leakage analysis based on models for transistor stacks. Modeling stacks has the advantage of using a single model across many gates there by reducing the number of models that need to be characterized. Our experiments on 15 different gates show that we needed only 23 models to predict the leakage across 126 input vector combinations. We investigate the use of neural networks for the combined PVT model, for the stacks, which can capture the effect of inter die, intra gate variations, supply voltage(0.6-1.2V) and temperature(0 - 100°C) on leakage. Results show that neural network based stack models can predict the PDF of leakage current across supply voltage and temperature accurately with the average error in mean being less than 2% and that in standard deviation being less than 5% across a range of voltage, temperature. © 2008 IEEE.

Proceedings of the IEEE International Frequency Control Symposium and Exposition

Voltage and temperature scalable standard cell leakage models based on stacks for statistical leakage characterization

We investigate the feasibility of developing a comprehensive gate delay and slew models which incorporates output load, input edge slew, supply voltage, temperature, global process variations and local process variations all in the same model. We find that the standard polynomial models cannot handle such a large heterogeneous set of input variables. We instead use neural networks, which are well known for their ability to approximate any arbitrary continuous function. Our initial experiments with a small subset of standard cell gates of an industrial 65nm library show promising results with error in mean less than 1%, error in standard deviation less than 3% and maximum error less than 11% as compared to SPICE for models covering 0.9-1.1V of supply, -40°C to 125°C of temperature, load, slew and global and local process parameters. Enhancing the conventional libraries to be voltage and temperature scalable with similar accuracy requires on an average 4x more SPICE characterization runs. © 2008 IEEE.