Engineering and Measurement of nsquid Circuits

Transcription

1 Engineering and Measurement of nsquid Circuits Jie Ren Stony Brook University Now with, Inc.

2 Big Issue: power efficiency! New Hero: Reversible Computer No dissipation limit. Quantum Computer Matthew Neeley, et al., Nature(2010) (Reversible inherently) Qubits, faster algorithm. Optical Computer researcher.ibm.com/view_project.php?id=2757 (Hybrid Computer) Faster, higher bandwidth. 1

3 nsquid: Reversible Computing Gate nsquid DC-SQUID nsquid Enengy Evolution Increasing ϕ c ϕ + ϕ - P1 V. K. Semenov, G. V. Danilov, and D. V. Averin, IEEE Trans. Appl. Supercond., J. Ren, V. K. Semenov, Yu. A. Polyakov, D. V. Averin, and J. S. Tsai, IEEE Trans. Appl. Supercond.,

4 Ic of 8-nSQUIDs Shift Register 1 P1 = 0 2 P1 = 1.0 δϕ c (Φ 0 ) 3 P1 = 2.0 δϕ c (Φ 0 ) The evolution of Ic modulation of the 8 nsquids shift register with increasing effect of differential flux in nsquids. δϕ c (Φ 0 ) 3

5 Two Versions of nsquids Reversible Circuits Shift Register Flux Generator Readout SQUIDs Nanoampere Meter 5 mm x 5 mm chips fabricated at J C = 30 A/cm 2 J. Ren and V. K. Semenov, IEEE Trans. Appl. Supercond, vol. 21, pp ,

6 Measurement Setup Contact Helmholt Pads z coils SQUID coils Y HeaterChip Z Holder X Main coil Probe with 3-D Helmholtz coil set up, for measurement in liquid Helium Heater Shield bases with the chip holder mounted on a second stage of a cryocooler 5

7 Flux Generator Transformer in RC08 chip Vortex pumper in LJJs chip 6

8 DC SQUID: nsquid State Readout Weakly coupled DC SQUID (coupling coefficiency ~ 0.02) 7

9 SQIF: Nano-Ampere Meter E E th = Φ 0 I = E Φ = (ln 2 / Φ ) k T th th 0 0 B = k Tln 2 At T = 4.2 K I th = 0.02μA B I 8

10 Energy Dissipation Measurement Measurement of the energy dissipation (in fact, dc current flowing via the circuit.): Current per 8-nSQUID shift register is 0.05 μa, which is 2.5 times of thermodynamic threshold (0.02 μa). Dissipation per one nsquid is 3 times less than the threshold. 9

11 Standard IC Process Crossing section along the red path in layout 4 superconducting wiring layers (M0 M3) 1 Josephson junction definition layer 1 resistor layer (Mo,Ti/PdAu, MoNx), R2 3 insulating layers of interlayer dielectric (SiO 2 ) + 1 anodization layer (Al 2 O 3 +Nb 2 O 5 ) 1 layer (Ti/Pd/Au) of contact metallization, R3 Details of design rules and fabrication process can be found on: 10

12 Fabrication Upgrade Higher Resolution New Photolithography Machine Cannon EX-4, 5X reduction stepper. Resolution to 0.25 µm Current Dual-Jc Design Library J c = 1.0/4.5 ka/cm 2 DFF: 4JJs Reduction: Area: 6.7 DFF: 4JJs New Dual-Jc Design Library J c = 4.5/20 ka/cm 2 11

13 Fabrication Upgrade More Wiring Layers 6 Wiring Layers J C = 4.5 ka/cm 2 Crossing section along the red path in layout 6 superconducting wiring layers (MN2, MN1, M0 M3) 2 resistor layer (R1, R2) More wiring layers increase circuit uniformity and further reduce the circuit size. 12

14 New Designed Long JJs (OLD) 1.0 μm minimal JJ size JC = 1 ka/cm2 77 JJs in the ring 2175 x 980 μm2 100 μm (NEW) 0.5 μm minimal JJ size JC = 4.5 ka/cm2 100 μm 144 JJs in the ring 2630 x 500 μm2 13

15 New Majority Gate (OLD) 1.0 μm minimal JJ size J C = 1 ka/cm 2 (NEW) 0.5 μm minimal JJ size J C = 4.5 ka/cm 2 Cell size: 2685 x 2500 μm 2 Return JJs occupy large area Cell size: 975 x 370 μm 2 Extra wiring layers simplify the communication among different data lines Largely reduced area will eliminate huge difficulty in measurement, especially defluxion. 14

16 Conclusion Design and Measurement of operational nsquids reversible circuits are presented. All circuits are designed using usual microelectronics design tools and are fabricated by a commercially available foundry. New fabrication with higher resolution and more superconducting wiring layers will strongly improve the nsquids circuit functionality and further reduce the energy dissipation. 15

17 Acknowledgement SUNY at Stony Brook Prof. Vasili K. Semenov Dr. Yuri Polyakov Prof. Dmitri V. Averin Inc. Fabrication team: Sergey Tolpygo, Daniel Yohannes, John Vivalda, Rick Hunt and Dave Donnelly. 16

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22 Josephson Junction Circuit as Basic Computer Element Energy Profile of the Element 1 ( π) ( ) U( x) = Φ /2 L [ x f /2+ λcos x] f : governs the value of the well asymmetry. λ: changes the height of the energy barrier. Left column: reversible switching from one stable state to another one. Right column: rapid jump of x in case of improper biasing K.K. Likharev, Classical and quantum limitations on energy consumption in computation, Int. J. Theor. Phys., vol. 21, p. 311,

23 nsquid is the Basic Gate U ( ϕ ) Φ I /2π 0 c Symmetric 2-JJ SQUID (I c1 =I c2 =I c ; L 1 =L 2 =L) Large negative mutual coupling (-m=-m/l) U( ϕ, ϕ ) Φ c e = + 0Ic / 2π l l+ 2 ( ϕ ϕe) = 2cosϕc cosϕ l ( π 1 ) ( ) 0 + ( ϕ ϕ ) ( ~ 0 ϕ + ϕ c ) 2 2 U =Φ/2 L [ x f /2+ λ cos x ] l ( ϕ ϕ ) 2cosϕ cosϕ Φ 0 ϕc = VDCt 2π ϕ± = ( ϕ1± ϕ2)/2 l = 2 π IC L/ Φ0 l = l(1 ± m) ± + 22

24 Two Strings of nsquids Data are sitting on the top of travelling vortices ( painted vortices), which are recycled by the ring. Domains occupy about 4 cells and move along the shift register with a constant speed (strictly proportional to V Cl ). Each string contains 8 nsquids. Jc=30 A/cm2. NOT gate: twist of two wires which provide magnetic coupling between two nsquids. 23

25 Long JJs I-V Curve Dashed Lines: theoretic fitting. Best fitted bias resistor is 7 times larger than its real value inductance Lr and Lb 24

26 Measurement of DC Current (Energy Dissipation) by SQIF E = Φ 0 I Eth = kbtempln 2 I = E Φ = (ln 2 / Φ ) k Temp th th 0 0 B At Temp=4.2 K I th =0.02μA Current is measured by SQIF. Right figure shows the measurement of Idc v.s. Iv while applying different external flux (legend in μa) into the circuit