Submicron CMOS: Device Modeling, Challenges, and Future Trends

About VLSI

1. AY-2025-2026 ODD SEM Department of ECE Session - 1 Mixed Signal IC design 22vls3505 Topic: Submicron CMOS

2. AIM OF THE SESSION To provide an in-depth understanding of submicron CMOS technology, including device modeling, process flow, and its application in digital and analog circuit design. To enable students to apply CMOS principles in designing and analyzing both digital logic blocks and analog building blocks using modern submicron processes. INSTRUCTIONAL OBJECTIVES This Session is designed to: Explain the CMOS process flow and identify key fabrication steps including capacitor and resistor formation. Describe how MOSFETs function as switches in digital circuits and analyze delay elements and adder circuits. Illustrate analog design principles such as biasing, operational amplifier configuration, and key noise sources. Relate the role of compact models and short-channel effects to performance in submicron CMOS technologies. LEARNING OUTCOMES At the end of this session , you should be able to: Analyze and design basic digital and analog circuits using submicron CMOS models. Interpret CMOS process flow diagrams and recognize how passive elements like capacitors and resistors are integrated on-chip. Evaluate the impact of process and device-level parameters on the performance and noise behavior of analog and digital circuits.

3. 3 CMOS = Complementary Metal Oxide Semiconductor Submicron CMOS: technologies < 1 µm (e.g., 0.25µm, 0.18µm, 90nm, 45nm, etc.) Applications: microprocessors, memory, mobile devices Benefits of scaling: Faster switching speed Lower power consumption Increased integration density Introduction to Submicron CMOS Fig: Devices examples in 180nm: a) Basic template layout and, b) Inverter cells I) STD and II) ELT-based Fig: C ore of the integrated circuit

4. 4 Moore’s Law and the Need for Scaling Fig: Moore’s Law Trend: Transistor Size Shrinking Over Time (1950–2020) Moore's Law: Transistor count doubles every 2 years. Technology node shrinkage faster smaller cheaper Scaling improves performance but introduces new challenges Voltage scaling slows down due to leakage and reliability issues

5. 5 Scaling Challenges in Submicron CMOS Fig: Short Channel Effects in MOSFETs Short-channel effects (SCEs): Threshold voltage roll-off Drain-Induced Barrier Lowering (DIBL) Hot carrier effects Increased leakage current & Power density increases Variability and Reliability issues

6. CMOS Device Modeling – Need and Types Need for accurate models in circuit design Types of models: Long-channel models (e.g., SPICE Level 1/2 – outdated) BSIM3/4 – includes SCEs, mobility reduction, leakage EKV Model – compact, good for analog Models used in CAD tools like Cadence, Synopsys, TCAD Fig: Hierarchy of process, device, and circuit simulation.

7. FinFETs and Submicron Structures Transition from planar CMOS to 3D structures: FinFET : Fin-shaped channel for better control Gate-All-Around (GAA): Improved electrostatics High-k/Metal Gate, SOI (Silicon-on-Insulator) Used in 22nm, 14nm, 7nm and beyond (a) (b) Fig: Structure of (a) Planar MOSFET and (b) FinFET

8. Modeling Submicron CMOS in Circuit Design Models must capture: Mobility degradation Gate leakage SCEs and DIBL BSIM4 used in SPICE tools for accurate results Verilog-A for custom models TCAD used for device-level simulation → data fed into SPICE models Fig: Flowchart for Simulation Model

9. Conclusion and Future Trends Submicron CMOS drives modern electronics Key is balancing performance, power, and area (PPA) Future: CFET (Complementary FET) 3D stacked transistors AI-assisted chip design Need for improved models and tools Fig: Evolution of Transistors

10. Conclusion and Future Trends Hands-On Tools for Submicron CMOS Synopsys Sentaurus (TCAD) Cadence Spectre, Virtuoso Silvaco ATLAS, SmartSpice Python for compact model fitting

11. THANK YOU Team – LOW POWER VLSI Design 11 Prepared by Dr. K.Girija Sravani