The One-Transistor, One-Capacitor (1T1C) Dynamic Random Access Memory (DRAM), and its Impact on Society
R. Jacob Baker Department of Electrical and Computer Engineering Boise State University 1910 University Dr., ET 201 Boise, ID 83725 [email protected]
Abstract – Memory technology development, in particular dynamic random access memory (DRAM), has been the greatest driving force in the advancement of solid-state technology for integrated circuit development over the last 40 years. The origin of DRAM circuits and technology can be traced to Dr. Dennard’s Patent (Number 3,387,286) granted on June 4, 1968. This truly visionary work, using a single transistor and capacitor (the 1T1C), is one of the most manufactured devices in the history of mankind. This talk will review the impact of his invention and discuss the brilliance of Dr. Dennard for conceiving the invention of the 1T1C cell prior to the maturity of metal oxide semiconductor (MOS) technology and in the face of critics that may have likely asked “why in the world would we want a memory, DRAM, that forgets its’ contents!?”
Baker 1 Let’s Step Back in Time
What are the following (hint: they were found in your local supermarket in the 50s, 60s, and early 70s)
Photos taken from ebay.com
Baker 2 Semiconductor-based Electronics were still new during this period of time
Does anyone remember the birth of the transistor radio? Below is seen the 2-transistor Furtura transistor radio (ca. 1955) 9 Note the output is via an earphone 9 Also note the schematic (not many, if any, consumer electronics products today come with a schematic)
Photos taken from ebay.com Baker 3 Evolution of the Transistor Radio
These were a big deal both because they were portable (something not practically possible with vacuum tube radios) and because they used a new technology (solid-state devices that didn’t wear out)
Photos taken from ebay.com Baker 4 Growing Complexity
Note the use of bipolar junction technology to replace vacuum tubes
Photo taken from ebay.com Baker 5 What was going on with memory storage during this time?
Dominated by the magnetic core memory seen below During the 1960s solid-state memory was developed based on the BJT 9 Ultimately wasn’t successful (compared to MOS-based memory)
1 mm
Image from wikipedia.org
Baker 6 So why is Dr. Dennard’s invention such a big deal?
During the excitement of bipolar technology replacing vacuum tubes in most electronic devices he filed an invention disclosure on July 14, 1967 that 9 Used metal-oxide-semiconductor (MOS) technology 9 Proposed a memory, the one-transistor, one-capacitor (1T1C cell), that forgets its contents! Why is using MOS technology such a big deal over bipolar? 9 MOS technology is scalable! 9 Another significant contribution from Dr. Dennard’s is scaling theory. Why is a memory that forgets its contents such a big deal? 9 It’s small! 9 It’s fast!
Baker 7 Dennard’s Scaling Theory*
Predicted that MOS devices would continue to shrink in size (scale) over time 9 Higher density 9 Faster 9 Low power Also discussed how interconnect would scale 9 RC times of the lines don’t scale but as distances shrink delays drop
* Dennard, R.H.; Gaensslen, F.H.; Rideout, V.L.; Bassous, E., and LeBlanc, A.R., “Design of ion-implanted MOSFET's with very small physical dimensions,” IEEE Journal of Solid-State Circuits, Volume 9, Issue 5, Oct 1974, pp. 256 - 268
Baker 8 Scaling Theory
Scaling from Dennard’s paper 9 Device and Circuit Scaling 9 Interconnect Scaling 9 Scale parameter is about 1.4 (1/κ = 0.7)
Baker 9 The One-Transistor, One-Capacitor (1T1C) Dynamic Random Access Memory (DRAM) cell
The array is formed with word (row) and column (bit) lines
Baker 10 Folded and Open Arrays
The open array
Baker 11 Folded and Open Arrays
The folded array
Baker 12 The Folded Array
Baker 13 Further Reduction in Cell Size
Sharing the bitline contact
Baker 14 Mbit Pair: Folded Array
Baker 15 Folded Array Cell Size
Baker 16 Open Array: 6F2
Baker 17 Array Block
Baker 18 The 1T1C DRAM Cell
ACT
Row 1 1-transistor, 1-capacitor (1T1C) DRAM Cell
Row 2
EQ
VDD/2
NLAT
Col 1
I/O I/O
Baker 19 SEM Photo of a Modern DRAM Array
Baker 20 How is DRAM used today?
Workstations Personal Digital Assistants Units - 1.69M Units – 8.9M DRAM – 5,741MB/unit average DRAM - 65MB average DRAM Revenue - $1,164M DRAM Revenue - $698M Source: iSuppli Source: iSuppli
PC Servers, Enterprise Units – 0.91M DRAM – 24,581MB Notebook DRAM Revenue - $2,684M Computers Source: iSuppli Units - 51M Desktop Computers DRAM – 510MB Units – 150M DRAM Revenue - $3,105M DRAM – 560MB Source: iSuppli DRAM Revenue - $10,048M Source: iSuppli
Memory Upgrades Printers Units – 87M Units - 112M DRAM – 295MB DRAM – 35MB DRAM Revenue - $3,060M DRAM Revenue - $156M Source: iSuppli Source: iSuppli
Baker 21 Communications and Networking Market
Cellular Phones SetTop Boxes Cable Modems Units - 740M Units – 62M Units – 15.7M DRAM – 5MB DRAM – 56MB DRAM – 8MB Flash – 87MB Flash – 2MB
DSL Modems Cellular Base Stations Units – 55M Units - 0.35M DRAM – 8MB DRAM - 256MB Flash –2MB Flash – 5112MB
LAN Switches LowEnd to MidRange Routers Units – 113.5M Units – 1.5M DRAM – 15MB DRAM – 406MB
Sources: iSuppli, Gartner, Portelligent, Instat
Baker 22 DRAM Demand by End-Use Application
100% Industrial Automotive
Consumer Mobile Communications 80% PC Graphics Wired Other Data Communications Processing* 60% Upgrade Modules Entry Level Servers (x86)
40% Mobile/Notebooks
20% Megabits of Total Percent Desktop PC
0% 2004 2005 2006 2007 2008 2009
*Other Data Processing includes mainframe servers, enterprise servers, workstations, handheld PCs, storage cards, printers, and internet appliances
Baker 23 Worldwide DRAM Shipments by Type
100% 5 1 1Gb 2Gb DDR3 2 Mb DDR2 90% D 1Gb DDR3 D R 80%
70% 128Mb 512 Mb DDR2 RDRAM 60% 512Mb 256Mb DDR DDR3 50% 2 56 M 40% b SD 128 Mb DDR 30% 64Mb DDR 1 20% 28 M b S Percent of Total Megabytes Produced Megabytes Total of Percent 64Mb EDO DR 64M 10% b SD RAM 16Mb SDRAM FP/EDO 0% 2002 2003 2004 2005 2006 2007 2008 2009
Baker 24 100% DRAM Technology Trends
90%
80%
70%
60%
50% DDR3 DDR2 40%
Units DDR SDRAM 30%
20%
10%
0% 2002 2003 2004 2005 2006 2007 2008 2009 2010
Baker 25 DRAM Density Trends
100%
90%
80% 4 Gb
70% 2 Gb 1 Gb 60% 512 Mb 50%
Units 256 Mb 128 Mb 40% 64 Mb 30% 16 Mb 20%
10%
0% 2002 2003 2004 2005 2006 2007 2008 2009 2010
Source: IDC, Isuppli, Gartner, IC Insights Q106
Baker 26 Historical PC Market Growth
60,000,000 35% 30% 50,000,000 25% 20% 40,000,000 15% 30,000,000 10% 5% 20,000,000 0% Units in Millions in Units -5% 10,000,000 Growth over Year Year -10% 0 -15% 1Q95 3Q95 1Q96 3Q96 1Q97 3Q97 1Q98 3Q98 1Q99 3Q99 1Q00 3Q00 1Q01 3Q01 1Q02 3Q02 1Q03 3Q03 1Q04 3Q04 1Q05 3Q05E Grand Total Grand Total
Baker 27 Price per Bit Cycles
100,000.00 Historically Price per Bit has 1975 1977 declined by an average of 9% 10,000.00 1974 every quarter 1979 1976 (1974-2005) 1981 1978 1983 1,000.00 1980 1985 1982 1987 1984 1989 100.00 1991 1993 1986 1988 1995 1990 1994 10.00 1992 1997
1996 1999 1.00 Price per Bit (Milicents) per Price 1998 2001 2000 2003 2005 0.10 2002 2004 0.01 1 100 10,000
12 Cumulative Bit Volume (10 ) 1,000,000 100,000,000
Source: Gartner, 05/05
Baker 28 Americas DRAM Unit Shipments by Density
2,000.0
1,800.0
1,600.0 1Gb 1,400.0
1,200.0 512Mb
1,000.0 64Mb Millions of Units 800.0 256Mb
600.0 128Mb 400.0
200.0
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010
1Mbit 4Mbit 16Mbit 64Mbit 128Mbit 256Mbit 512Mbit 1Gbit 2Gbit 4Gbit 8Gbit
Baker 29 256Mb Equivalent Unit DRAM Shipments
256Mb Equivalent Units Shipped (K Units)
700,000 Total 256Mb EU 100% 12/12 Growth 90% 600,000 80% 500,000 70% 60% 400,000 50% 300,000 40%
200,000 30% 20% 100,000 10% 0 0% Jul-98 Jul-99 Jul-00 Jul-01 Jul-02 Jul-03 Jul-04 Jan-99 Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Apr-98 Oct-98 Apr-99 Oct-99 Apr-00 Oct-00 Apr-01 Oct-01 Apr-02 Oct-02 Apr-03 Oct-03 Apr-04 Oct-04 Apr-05
Baker 30 DRAM Applications with the Highest Unit Growth Rates
(CAGR 2004 – 2008)
Entry-Level PC Servers
Internet Appliances
Mobile PCs
Wireless LAN Client Access
Wireless LAN Access Point/Bridge
SAN Switches
MP3 player
Flash Storage Cards
Digital TVs
DVD Video Recorder
0% 10% 20% 30% 40% 50% 60%
Baker 31 Fastest Growing DRAM Consumption
Enterprise Servers (CAGR 2004 – 2009) Upgrade Module
Handheld Computers
Mobile PCs
Deskbound PCs
Entry-Level PC Servers
Workstations
Internet Appliances
Remote Access RAC & RAS
Mobile Handsets
0% 20% 40% 60% 80% 100%
Baker 32 Summary Overview
DRAM chips are found in virtually every computer in use today. Looking at the simplicity of the 1T1C cell one might wonder about the significance of this invention by modern day standards. However, if it is remembered that this idea was conceived back in the 1960s before MOS technology had matured enough for production or the idea that circuits could be “dynamic” (only operating correctly for a short period of time) the significance of the invention becomes clear. What is usually not mentioned when talking about Dr. Dennard’s contributions to the 1T1C memory cell is his contributions of seeing this idea to product (the true test for any practical electrical engineer). The MOS process development (and the concerns for defects and reliability which have a drastic effect on the dynamic operation of MOS circuits) and supporting circuitry are also extremely important contributions that Dr. Dennard made while at IBM. In summary, Dr. Dennard cut the path for modern DRAM memory chip developments.
Baker 33