Electrical characterisation of nanoscale samples & biochemical interfaces: methods and electronic instrumentation Measuring currents below 4K Cryogenic electronics Giorgio Ferrari Dipartimento di elettronica e informazione Politecnico di Milano Milano, November 27 2014 Motivation 1: enviroment temperature Example: Astronomical applications Moon minimum temperature: 40 K Space background: 3K • Cryogenics electronics to avoid heating units • mid- and far-infrared detectors require temperature below 5K Conceptual image of JAXA/SPICA. 2 Cryogenic electronics - G. Ferrari 1 Motivation 2: improving the system • • • • 1m less thermal fluctuations low drift Ultra High Vacuum dI/dV prop. to the sample density of states: energy resolution ≈ kBT 10mK 3nm 3 Cryogenic electronics - G. Ferrari Y.J.Song et al., Rev. Sci. Instr., 81, 121101 (2010) Example: STM / SPM at 10mK graphene, profile ±20pm: (T=13mK) Motivation 3: quantum devices Ex.: spectroscopy of a single As atom in FinFET T= 1.6K (kBT= 138 µeV) E. Prati lesson G. P. Lansbergen et al.,Nature Physics 4, 656 - 661 (2008) 4 Cryogenic electronics - G. Ferrari 2 Experimental set-up to study quantum devices RF VOUT CP≈1nF ≈ 2 meter 12T Cryomagnet 270mK I RMS T=300K T=1.5K B 2πeN C P B = 3 Bandwidth = T=0.3K 3 2 GBWP 10 ⋅ 2πR f C P CP reduces performances E. Prati, CNR laboratory Sample Cryogenic electronics - G. Ferrari 5 Experimental Set-up RF VOUT CP≈1nF 12T Cryomagnet 270mK T=300K T=1.5K B T=0.3K Sample 6 RF Bandwidth Resolution 10GΩ 12Hz 1GΩ 130Hz 15fARMS 186fARMS 100MΩ 718Hz 1.06pARMS 10MΩ 6.34kHz 14.7pARMS 1MΩ 100kHz 750pARMS E. Prati, CNR laboratory Cryogenic electronics - G. Ferrari 3 Experimental Set-up RF CP≈1nF VOUT eN 12T Cryomagnet 270mK T=300K Si ,eq = 4kT + eN2 ω 2C P2 RF T=1.5K Both drastically lowered B T=0.3K Sample 7 how does electronics work at few Kelvin? Cryogenic electronics - G. Ferrari http://fog.ccsf.cc.ca.us/~wkaufmyn/ Semiconductor freeze-out 8 ionization energy for phosphorus: 45meV T≈ 70K log n n ≈ ND Cryogenic electronics - G. Ferrari 4 Freeze-out: consequences silicon bipolar transistors silicon JFET transistors almost all commercial OpAmp … cannot be operated below ≈ 40-70K !!! G What about MOSFET? S D SiO2 heavily doped region moderately doped region n+ n+ p-well Cryogenic electronics - G. Ferrari 9 increasing doping level The impurity band model ≈1019 10 Akturk et al., Silicon qubit For N ≈ 1019 cm-3 → interactionECof impurity atoms workshop, 2009 band of energies Ev Overlapping in degenerate Overlapping inwill degenerate semiconductor make it semiconductor make it behave more like awill conductor behave more like a metal than a semiconductor than a semiconductor Cryogenic electronics Ferrari E. Prati et al., Nature- G.Nanotechnology 7, 443–447 (2012) 5 http://www.extremetemperatureelectronics.com Degenerate semiconductor Cryogenic electronics - G. Ferrari 11 Electronics below the freeze-out temp. electric field creates a conductive channel! G S SiO2 no freeze-out: conductive freeze-out: insulator D n+ n+ p-well Silicon (standard) MOSFET operates below 40K! Many GaAs devices operate at cryogenic temperature: degenerate at 1016 cm-3 Limitation: small (and expensive) scale integration 12 Cryogenic electronics - G. Ferrari 6 MOSFET operating at 4K Standard analog CMOS Technology 3.3V, 0.35µm PMOS 50µm / 0.7µm IDRAIN 0.0 0.0 -2.0m -4.0m -6.0m IDRAIN -2.0m 300K 4.2K -4.0m -6.0m -8.0m -8.0m -10.0m -10.0m -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 T = 4K -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 VGATE VDRAIN very similar to the room temperature behavior! 13 Cryogenic electronics - G. Ferrari Effects of low temperature • reduction in electron - phonon scattering → increase in carrier mobility • freeze-out of the dopants in the substrate → increase of the threshold voltage 14 Engelectronics et al. Silicon Qubit Cryogenic - G. Ferrari Workshop ‘09 7 MOSFET operating at 4K: problems Ghibaudo, Balestra, “Low Temperature characterization of Silicon CMOS Devices”, 1995 Y. Creten et al., IEEE J. Solid-State circuits, p. 2019 (2009) Cryogenic electronics - G. Ferrari 15 MOSFET operating at 4K: problems kink effect, hyteresys, slow charging of traps… G G S D S SiO2 n+ SiO2 n+ p-well impact ionization → accumulation of holes → VT decreases 16 D n+ n+ p-well slow charging of shallow traps at the SiSIO2 interface → free charge decreases Cryogenic electronics - G. Ferrari 8 Problems are tech and size dependent PMOS=50umx0.7um …and no models from foundry! SOLUTION: Preliminary extraction of the model parameters for the target technology Cryogenic electronics - G. Ferrari 17 Design rule 1 MOS parameters strongly depend on the size Experimental characterization of few MOS sizes series or parallel combinations of these basic transistors W/2L W/L W/L W/L 2W/L W/L less conductive MOS 18 more conductive MOS Cryogenic electronics - G. Ferrari 9 pay attention to mismatch: deterioration of mismatch by a factor of 2-3 at low temperature compared with room temperature. 19 K. Das et al. EEE Symposium on Circuits and Systems, 2010 Design rule 2 Cryogenic electronics - G. Ferrari Design rule 3: avoid subthreshold Eng et al. Silicon Qubit Workshop ‘09 VT mismatch of 1mV: 20 Cryogenic electronics - G. Ferrari 10 Design rule 4 pay attention to the dynamic range: • • • • VT,n from 0.45V to 0.7V VT,p from -0.7V to -1.4V Power supply: 3.3V no subthreshold stack up few transistors! no deep-submicron technologies (reduced supply voltages) and kink effect limit the VDS! Cryogenic electronics - G. Ferrari 21 Noise γ 2 Thermal noise: en = 4kT g m T , gm → noise (0.1nV/sqrt(Hz)) Flicker noise: sometime increases, sometime decreases... Noise (A/sqrt(Hz)) Id=100uA 100p 10p T=4K T=7K T=15K T=20K T=30K T=110K T=135K T=150K T=300K dominant noise up tens of MHz T 1k 22 pmos 50/0.7 Frequency (Hz) 10k Cryogenic electronics - G. Ferrari 11 Cryogenic transimpedence amplifier Standard structure: Noise equivalent to 1.7GΩ @ 300K 250fF IIN 22.5 MΩ VOUT Capacitor: Resistor: 23 Cryogenic electronics - G. Ferrari Cryogenic transimpedence amplifier 1.2mm IIN 22.5 MΩ 700µm 250fF VOUT CMOS Technology 3.3V 0.35µm nMos: 50µm/1.4µm pMos: 50µm/0.7µm VDD 200µm 0.7µm IP 200µm 0.7µm 650µm 0.7µm VOUT V- 2500µm 1.4µm V+ I1 I2 VSS 24 Cryogenic electronics - G. Ferrari 12 1.5 1.0 Gain, linearity and bandwidth match the simulations T=4K 0.5 0.0 -0.5 -1.0 -1.5 -75n -50n -25n R=22.54MOhm 0 25n 50n 75n Input current [A] Transimpedence (VOUT/IIN) Output voltage [V] Measurements at 4 Kelvin F-3dB=32kHz 10M T=4K 1M 100k Cryogenic electronics - G. Ferrari 25 10k 10 100 1k 10k 100k 1M Frequency (Hz) Input Noise (A/sqrt(Hz)) Measurements at 4 Kelvin Quantum dots with a single ion implanted 1p T=4K 100f Measured Theoretical S 10f D 1f 10 100 1k 10k Frequency (Hz) 100k Single charge state sensing • 2.33pARMS resolution • 32kHz Bandwidth ≈ 30 times better of RT 26 Mazzeo et al APL 2012 Cryogenic electronics - G. Ferrari 13 Temperature dependence 4K 300K Iin - Vout + Output Voltage (V) Rf 0.4 0.3 0.2 0.1 0.0 -0.1 -0.2 -0.3 -0.4 300K 280K 260K 225K 200K 165K 125K 85K 60K 46K 20K 15K 11K 8K 4K T -50.00n -25.00n 0.00 25.00n 50.00n Input current (A) • Opamp works in a wide temperature tange • The gain depends on temperature (RF) Cryogenic electronics - G. Ferrari 27 Current-mode output Rf 8.6MΩ + Rout Iout Vout 123kΩ Output Current (A) Iin 10.0µ 4K 300K 5.0µ 4K 6K 8K 11K 33K 60K 100K 150K 220K 300K 0.0 -5.0µ -10.0µ -100.0n -50.0n 0.0 50.0n 100.0n Input current (A) • Simple solution • Current gain = 70 • Better temperature performances 28 Cryogenic electronics - G. Ferrari 14 Summary • Cryogenic CMOS circuits are feasible • • transimpedance amplifiers (BW=30kHz, noise= 2.3pARMS) ADC (Ockan et al., RSI 2010 and 2012) • Anomalous behavior of the MOSFETs • • 29 preliminary characterization of the transistors (and R) design techniques to limit effects Cryogenic electronics - G. Ferrari 15
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