LFSR Test Pattern Crosstalk in Nanometer Technologies Dieter Treytnar,, Michael Redeker, Hartmut Grabinski and Faïez Ktata Laboratory for Information Technology University of Hannover, Germany
Outline! Introduction! Line Parameters! Linear Feedback Shift Register! Simulation Results! Summary 6th Workshop on Signal Propagation on Interconnects 22 2
Introduction SIA predicts a very aggressive path of technologies! Technology will decrease from 5 nm (today) down to 35 nm (year 22)! Number of gates will increase from 22 M up to 2, M! Frequency will increase from.4 GHz up to 8 GHz! Power Voltage will decrease from.2 Volts down to.45 Volts 6th Workshop on Signal Propagation on Interconnects 22 3
How does scaling in nanometer technologies affect the quality of signals? How stable are test patterns against crosstalk? 6th Workshop on Signal Propagation on Interconnects 22 4
Contents! Introduction! Line Parameters! Linear Feedback Shift Register! Simulation Results! Summary 6th Workshop on Signal Propagation on Interconnects 22 5
Line Parameters Geometric Data for Copper Lines in Metal 5 technology 5nm nm 7nm 5nm 35nm width [µm].33.22.6..8 spacing [µm].8.55.39.26.2 height [µm].92.77.55.36.29 dist.. to subst. [µm] 6.54 5.735 4.725 3.87 3.345 Source: Int. Technology Roadmap for Semiconductors 999 6th Workshop on Signal Propagation on Interconnects 22 6
Self Capacitance C' [pf/m] 3 25 2 5 5 technology.25.5..7.5.35 5 4 3 2 metal F Sub =. S/m 5 parallel copper lines Strong decrease in local wires Nearly constant in global wires 6th Workshop on Signal Propagation on Interconnects 22 7
Mutual Capacitance C' [pf/m] 6 4 2 8 6 4 2.25 technology.5..7.5.35 5 4 3 2 metal Saturation effect in smaller technologies 6th Workshop on Signal Propagation on Interconnects 22 8
Self Inductance L' [µh/m],6,4,2,,8,6,4,2, technology.25.5..7.5.35 5 4 3 2 metal Increasing L for smaller technologies 6th Workshop on Signal Propagation on Interconnects 22 9
Mutual Inductance L' [µh/m],4,2,,8,6,4,2, technology.25.5..7.5.35 5 4 3 2 metal Increasing L for smaller technologies 6th Workshop on Signal Propagation on Interconnects 22
Resistance 3 R' [kohm/m] 25 2 5 5.25.5 technology..7.5.35 5 4 3 2 metal Very strong increasing R for smaller technologies 6th Workshop on Signal Propagation on Interconnects 22
Resistance per unit length plays a very important role in the future Crosstalk effects have to be taken into account 6th Workshop on Signal Propagation on Interconnects 22 2
Contents! Introduction! Line Parameters! Linear Feedback Shift Register! Simulation Results! Summary 6th Workshop on Signal Propagation on Interconnects 22 3
Linear Feedback Shift Register I Future integrated circuits will likely be tested by self test strategies only (M.Rodgers, Intel; ITC 99) Most common built-in test pattern generator used in today s chip design is the LFSR An LFSR is very easy to implement and further on very powerful for self testing 6th Workshop on Signal Propagation on Interconnects 22 4
Linear Feedback Shift Register II Shift register with XOR feedback loop Dividing polynomial is primitive 6th Workshop on Signal Propagation on Interconnects 22 5
Linear Feedback Shift Register III timestep 2 3 4 5 6 7 8 9 2 3 4 5 6 = Bit Bit Bit 2 Bit 3 It can adopt 2 n - states (pseudo random patterns) Singular state: tstep n Bit Bit Bit 2 Bit 3 6th Workshop on Signal Propagation on Interconnects 22 6
Linear Feedback Shift Register IV LFSR produces ones and zeros so that very strong crosstalk arise 6th Workshop on Signal Propagation on Interconnects 22 7
Contents! Introduction! Line Parameters! Linear Feedback Shift Register! Simulation Results! Summary 6th Workshop on Signal Propagation on Interconnects 22 8
Simulation Results TP V() V(6) V(2) TP2 V(2) V(7) V(4) TP3 V(3) V(8) V(6) TP4 V(4) V(9) V(8) TP5 V(5) V() V(2) Z D copper, l = mm C L Simulated line system with a 5 bit LFSR 6th Workshop on Signal Propagation on Interconnects 22 9
7 nm technology Line Line 2 Line 3 6th Workshop on Signal Propagation on Interconnects 22 2
5 nm technology Line Line 2 Line 3 6th Workshop on Signal Propagation on Interconnects 22 2
35 nm technology Line Line 2 Line 3 6th Workshop on Signal Propagation on Interconnects 22 22
Crosstalk Effects! 7 nm technology - few crosstalk effects - fault free in the digital world! 5 nm technology - stronger crosstalk effects - propagation is dominated by delay effects! 35 nm technology - strong crosstalk effects - strongly increasing resistance - LFSR test patterns will be transmitted with errors 6th Workshop on Signal Propagation on Interconnects 22 23
What are the influences of coupling parameters in detail? 6th Workshop on Signal Propagation on Interconnects 22 24
Comparison 35 nm technology Purely resistive With coupling (L, C ) 6th Workshop on Signal Propagation on Interconnects 22 25
Conclusions! It is nearly impossible to transmit LFSR test patterns through a line system longer than mm beyond the 5 nm technology! Propagation through lines shorter than.5 mm can be expected to be fault free for the 35 nm technology! Delay due to higher resistances is an important problem in nanometer technologies! Crosstalk will further play an important role for LFSR testing in the future and has to be taken into account 6th Workshop on Signal Propagation on Interconnects 22 26
Possible Solutions Problems of testing monster chips can be reduced by...!...new test techniques (e.g. cellular automatas, chip partioning for testing)!...new line geometries (e.g. wave guides on chip)!...implementing long lossy lines in larger geometries (e.g. double the width and spacing) 6th Workshop on Signal Propagation on Interconnects 22 27
Thank you very much for your attention 6th Workshop on Signal Propagation on Interconnects 22 28