Semiconductor Memories Lecture 1: May 10, 2006 EE Summer Camp Abhinav Agarwal

Outline Concept/need of memory Parameters Types/classification Basic features Basic Cell circuits Peripheral circuitry

Concept Data storage essential for processing Binary storage Switches How do you implement this in Hardware?

Requirements Easy reading Easy Writing High density Speed, more speed and still more speed

Memory Chip Configuration

© Digital Integrated Circuits 2nd Memories Semiconductor Memory Classification Read-Write Memory Non-Volatile Read-Write Memory Read-Only Memory EPROM E 2 PROM FLASH Random Access Non-Random Access SRAM DRAM Mask-Programmed Programmable (PROM) FIFO Shift Register CAM LIFO

RAM Random write and read operation for any cell Volatile data Most of computer memory DRAM  Low Cost  High Density  Medium Speed SRAM  High Speed  Ease of use  Medium Cost

ROM Non-volatile Data Method of Data Writing Mask ROM  Data written during chip fabrication PROM  Fuse ROM: Non-rewritable  EPROM:Erase data by UV rays  EEPROM: Erase and write through electrical means Speed 2-3 times slower than RAM Upper limit on write operations Flash Memory – High density, Low Cost

Basic Cells DRAM SRAM

© Digital Integrated Circuits 2nd Memories Static CAM Memory Cell

© Digital Integrated Circuits 2nd Memories CAM in Cache Memory Address Decoder Hit Logic CAM ARRAY Input Drivers TagHit Address SRAM ARRAY Sense Amps / Input Drivers DataR/W

ROM Fuse ROM EEPROM Floating Gate

© Digital Integrated Circuits 2nd Memories MOS NAND ROM All word lines high by default with exception of selected row WL[0] WL[1] WL[2] WL[3] V DD Pull-up devices BL[3]BL[2]BL[1]BL[0]

© Digital Integrated Circuits 2nd Memories Non-Volatile Memories The Floating-gate transistor (FAMOS) Floating gate Source Substrate Gate Drain n + n +_ p t ox t Device cross-section Schematic symbol G S D

© Digital Integrated Circuits 2nd Memories Floating-Gate Transistor Programming 0 V - 5 V 0 V DS Removing programming voltage leaves charge trapped 5 V V 5 V DS Programming results in higherV T. 20 V 10 V5 V 20 V DS Avalanche injection

© Digital Integrated Circuits 2nd Memories A “Programmable-Threshold” Transistor

© Digital Integrated Circuits 2nd Memories Periphery  Decoders  Sense Amplifiers  Input/Output Buffers  Control / Timing Circuitry

© Digital Integrated Circuits 2nd Memories Row Decoders Collection of 2 M complex logic gates Organized in regular and dense fashion (N)AND Decoder NOR Decoder

© Digital Integrated Circuits 2nd Memories Hierarchical Decoders A 2 A 2 A 2 A 3 WL 0 A 2 A 3 A 2 A 3 A 2 A 3 A 3 A 3 A 0 A 0 A 0 A 1 A 0 A 1 A 0 A 1 A 0 A 1 A 1 A 1 1 Multi-stage implementation improves performance NAND decoder using 2-input pre-decoders

© Digital Integrated Circuits 2nd Memories Sense Amplifiers t p C  V  I av = make  V as small as possible smalllarge Idea: Use Sense Amplifer output input s.a. small transition

© Digital Integrated Circuits 2nd Memories Sense Amp Operation D V(1) V V(0) t V PRE V BL Sense amp activated Word line activated

© Digital Integrated Circuits 2nd Memories Differential Sense Amplifier Directly applicable to SRAMs M 4 M 1 M 5 M 3 M 2 V DD bit SE Out y

© Digital Integrated Circuits 2nd Memories Reliability and Yield

References Digital Integrated Circuits, 2 nd Edition, Jan Rabaey, Anantha Chandrakasan, Borivoje Nikolic Chapter Sedra & Smith, Microelectronic Circuits, 4 th Edition, Chapter 13  Section 13.9, 13.10, 13.11, VLSI Memory Chip Design, Kiyoo Itoh