Real-Time Reconfigurable Devices Implemented in UV-Light Programmable Floating-Gate CMOS
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Real-time reconfigurable devices implemented in UV-light programmable floating-gate CMOS by Snorre Aunet June 2002 A dissertation submitted to the Norwegian University of Science and Technology Faculty of Information Technology, Mathematics and Electrical Engineering in partial fulfillment of the requirements for the degree of Doktor Ingenipr. ii iii Abstract This dissertation describes using theory, computer simulations and labora tory measurements a new class of real time reconfigurable UV-programmable floating-gate circuits operating with current levels typically in the pA to fiA range, implemented in a standard double-poly CMOS technology. A new design method based on using the same basic two-MOSFET circuits extensively is proposed, meant for improving the opportunities to make larger FGUVMOS circuitry than previously reported. By using the same basic circuitry extensively, instead of different circuitry for basic digital functions, the goal is to ease UV-programming and test and save circuitry on chip and I/O-pads. Matching of circuitry should also be improved by using this approach. Compact circuitry can be made, reducing wiring and active components. Compared to earlier FGUVMOS approaches the number of transistors for implementing the CARRY’ of a FULL-ADDER is reduced from 22 to 2. A complete FULL-ADDER can be implemented using only 8 transistors. 2- MOSFET circuits able to implement CARRY’, NOR, NAND and INVERT functions are demonstrated by measurements on chip, working with power supply voltages ranging from 800 mV down to 93 mV. An 8-transistor FULL-ADDER might use 2500 times less energy than a FULL-ADDER implemented using standard cells in the same 0.6 fim CMOS technology while running at 1 MHz. The circuits are also shown to be a new class of linear threshold elements, which is the basic building blocks of neural networks. Theory is developed as a help in the design of floating-gate circuits. iv Preface I have had the great pleasure of working with UV-programmable floating- gate (”FGUVMOS”) circuits for a period. It has first and foremost been interesting and rewarding, but also hard work. Support from the surround ings has been of paramount importance: I am very grateful to my supervisors, professors Trond S$ther, NTNU, and Yngvar Berg at the University of Oslo. They gave great support at various levels, including moral support, in seeking financial support, making various decisions, and writing and discussing technological issues. Thanks also to associate professor Tormod Nj0lstad, Department of Physical Electronics, NTNU, for initiating my first meeting with FGU- VMOS circuits by arranging a trip to the Department of Informatics, Uni versity of Oslo. I would also like to thank the Microelectronics group at the Department of Informatics (Ifi), University of Oslo, for accepting me as an occasional coworker and guest during these years. Dag T. Wisland (Ifi) deserves thanks for SW-support and laboratory support during my visits to Ifi. Shevana Bianca Aquariux was of great help in many discussions. Associate professor Nancy Lea Eik-Nes gave help with writing of the manuscript. Thanks to professor Steinar Andresen, NTNU, for financial support for producing chips, going to conferences and more, through the Telecom 2005 programme. Thanks to Sverre Vegard Pettersen for taking the chip photos. Thanks also to colleagues at the Department of Physical Electronics, NTNU, for nice working conditions since May 1997, and lately the Depart ment of Computer and Information Science, NTNU. Thanks also to my family and friends for help, support and patience. Trondheim, June 2002 Snorre Aunet Contents Abstract iii Preface iv 1 Introduction 1 1.1 The neuron-MOS and FGUVMOS circuit concepts ............ 1 1.2 New real time reconfigurable floating-gate circuits ............ 5 1.3 Thesis outline ............................................................................. 9 2 Multiple-input UV-programmable MOSFETs and two-MOSFET circuits 11 2.1 MOSFETs................................................................................... 11 2.1.1 MOSFETs in weak inversion ..................................... 11 2.1.2 Floating-gate CMOS transistors ............................... 18 2.1.3 Single-input floating-gate MOSFETs......................... 21 2.1.4 Multiple-input floating-gate CMOS transistors ... 28 2.2 UV-programmable inverters .................................................... 31 2.3 A 2-MOSFET 3-input reconfigurable ”single-ended ” circuit 39 3 Floating-Gate UV-programmable MOSFETs 45 3.1 Implementation and layout of FGUVMOS transistors .... 45 3.2 Laboratory setup and UV -programming .............................. 52 3.3 Measurement Results................................................................. 59 3.4 MOSFET discussion ................................................................. 72 4 Floating-gate UV-programmable inverters 75 4.1 Implementation and layout of inverter .................................. 75 4.1.1 Simulation of the the FGUVMOS inverter ............... 75 4.1.2 Layout of the FGUVMOS inverter ............................ 81 4.2 UV -programming and test setup ........................................... 83 v vi CONTENTS 4.2.1 Basic information regarding UV-programming and test setup ....................................................................... 83 4.2.2 UV-programming taking from tens of minutes to many hours for a few transistors ........................................... 85 4.2.3 Additional information regarding UV-programming and test setup .............................................................. 85 4.3 Inverter measurement results................................................. 89 4.4 Simulation of maximum operational frequency as a function of Cn ............................................................................................. 96 4.5 Inverter discussion .................................................................... 104 5 Multiple-input floating-gate 2-MOSFET ”PMNM” circuits109 5.1 Implementation and layout of ”PMNM” elements ............... 109 5.1.1 P3N3 element ................................................................. 109 5.1.2 P5N5 element ................................................................. 112 5.1.3 "PMNM” layout ........................................................... 117 5.2 UV-programming and test setup of P5N5 element ................. 120 5.3 P5N5 results ............................................................................. 124 5.3.1 Simulation results ........................................................ 124 5.3.2 Measurement results.................................................... 124 5.4 PMNM discussion .................................................................... 131 6 Multiple-input floating-gate 2-MOSFET ”P1NM” circuits133 6.1 Implementation and layout of ”P1NM” elements ................ 133 6.1.1 P1N2 ............................................................................. 133 6.1.2 P1N3 ............................................................................. 137 6.2 UV-programming and test setup of the P1N3 element . 137 6.3 P1N3 results ............................................................................. 141 6.4 P1NM / PMN1 discussion ........................................................ 147 7 INVERTERS, ”P1NN” and ”PMNM” as building blocks 149 7.1 Basic digital functions ............................................................. 149 7.1.1 Generating Boolean functions using PMNM and P1NM building blocks .............................................................. 149 7.1.2 Simulation of a 4-transistor circuit able to generate SUM' and CARRY' ..................................................... 154 7.1.3 Area of a Boolean function generator using minimum transistors ....................................................................... 156 7.1.4 Discussion regarding FGUVMOS binary function gen eration ............................................................................. 157 CONTENTS vii 7.2 8-transistor FULL-ADDERs..................................................... 158 7.2.1 Implementation and layout of FULL-ADDERs . 158 7.2.2 Functionality and Power-Delay-Product simulations of 8-transistor FULL-ADDER..................................... 161 7.2.3 FULL-ADDER discussion ........................................... 164 7.3 D-Latch ...................................................................................... 169 7.4 6-transistor 3-bit ADC / Frequency synthesizer ................... 171 7.4.1 Implementation and simulation of ADC3 / Frequency Synthetisator ................................................................. 171 7.4.2 ADC / frequency synthesizer discussion ................... 174 7.5 Inverter-only based logic ........................................................... 175 7.6 Theoretical lower voltage bound and voltage gain ......................176 7.7 Implementing linear threshold functions ............................... 179 7.7.1 Linear threshold elements and neural networks . 179 7.7.2 Mathematical definition of the FGUVMOS linear thresh old gates ....................................................................... 180 7.7.3 Circuit complexity and costs of linear threshold gates 180 7.7.4 A new type of threshold gate..................................... 182 7.7.5 The pFET synapse transistor - for neural networks in hardware, or systems-on-a chip ................................ 182 7.7.6 FGUVMOS linear threshold elements