Ultrastable Low-Noise Current Amplifiers With Extended Range and Improved Accuracy

Ultrastable Low-Noise Current Amplifiers With Extended Range and Improved Accuracy (Ultrastable Low-Noise Current Amplifier ULCA) D. Drung and C. Krause Thanks to... Physikalisch-Technische Bundesanstalt (PTB) Berlin and Braunschweig, Germany PTB colleagues: M. Piepenhagen, M. Luther, M. Götz, E. Pesel, U. Becker, H. Scherer EU funding: JRP "e-si-amp" (15SIB08) This project has received funding from the European Metrology Programme for Innovation and Research (EMPIR) co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation programme. Outline: - Introduction - The standard 3 GΩ ULCA - Second ULCA generation - Conclusions 1

2012: Motivation for ULCA development Realization of ampere based on single-electron transport (SET) current sources I SET = 100 pa Goal: Measure 100 pa with 10-7 total uncertainty (k = 1, including type B) Total uncertainty: 10-17 A = 10 aa = 62 e/s PTB s CMC entry: 10 ppm standard uncertainty at 100 pa (capacitor charging) 1 GΩ standard resistor calibrated with NPL CCC: 1 ppm standard uncertainty Initial approach: CCC with >10 4 turns used as current amplifier SQUID serves as null detector 33 mm Two limitations expected: SQUID nonlinearity & low-frequency noise PTB 14-bit CCC (18276 turns) 2

New Approach: The ULCA Basic idea: Combine advantages of two technologies: CCC / semiconductor amplifier Use CCC for calibration at high current 10 na highest accuracy Use semiconductor amplifier for measurement at 100 pa lowest 1/f noise highest user-friendliness series production possible 23 cm 3

Basic ULCA Concept (a) Voltage Output I OA1 GND DUT I 3G ±44V ±5V OA2 3M 1000 I Output = VOUT 1M IRET V VOUT IOUT Output Signal Input stage OA1 provides 1000-fold current gain Thin-film resistor network with 3000 chip resistors (much better than thick-film) Output stage OA2 performs current-to-voltage conversion Voltage output: internal 1 MΩ metal-foil resistor A TR = V OUT / I = 1 GΩ 23 cm 4

Basic ULCA Concept (a) Voltage Output I OA1 GND DUT (b) Current Output I I OA1 GND DUT I 3G 3G ±44V ±5V OA2 3M 1000 I Output = VOUT 1M IRET V VOUT Output = IOUT ±44V ±5V OA2 3M 1000 I 1M IRET Rext IOUT Output Signal VOUT Output Signal V IOUT Input stage OA1 provides 1000-fold current gain Thin-film resistor network with 3000 chip resistors (much better than thick-film) Output stage OA2 performs current-to-voltage conversion Voltage output: internal 1 MΩ metal-foil resistor A TR = V OUT / I = 1 GΩ Current output: external resistor R ext = 0-100 MΩ (CCC coil or QHR possible) 5

The Standard 3 GΩ ULCA Powered by two batteries (one charged while the other used for ULCA supply) uninterruptible earth-free battery operation Well suited for current measurement & generation or resistance calibration Improved instrument for applications with fa to na currents Current range: ±5 na @ normal mode ±5 µa @ extended mode (output stage only) Excellent accuracy: < 0.1 ppm @ on-site calibration with PTB CCC < 1 ppm @ inter-lab comparisons Long-term stability: 2 ppm/yr @ one year after assembling 1 ppm/yr @ two years after assembling Applications: Calibration of current sources and meters Calibration of high-value resistors Small-current travelling standard High-accuracy measurements of SET pumps 6

Calibration of Picoammeter and Source Keithley 6430 picoammeter Keithley 263 current source Relative expanded uncertainty (k = 2) 10-1 10-2 10-3 10-4 11 h 300 cycles 11 h 300 cycles 11 h 300 cycles 3.5 h 100 cycles 10-5 3.5 h 10-6 10-7 1f Ammeter calibrations (K6430) CMCs of PTB ('capacitor charging') CMCs of PTB ('voltage across shunt') Calibrations with ULCA current source (3 month calibration interval) 100 cycles ULCA normal mode 3.5 h 1 h 100 cycles 30 cycles 1 h 30 cycles 1 h 30 cycles extended mode 1 h 30 cycles 10-1 10-2 10-3 10-4 Current source calibrations (K263) CMCs of PTB ('voltage across shunt') Calibrations with ULCA electrometer (3 month calibration interval) 5 min 2 cycles 5 min 2 cycles 10-5 5 min 10-6 10-7 1f ULCA normal mode 2 cycles 5 min 2 cycles 5 min 2 cycles 5 min 5 min 2 cycles 2 cycles extended 10f 100f 10p 100p 10n 100n 10f 100f 10p 100p 10n 100n 1p 1n 1µ 1p 1n 1µ Current / A Poster Tu-P20 by H. Scherer (Tuesday 15:00-16:00) Current / A 7

High-Accuracy Measurements on SET Pumps Two 3 GΩ ULCAs measure ±I SET V OUT measured against JVS Noise reduced by factor 2 Influence of DVM negligible 10 3 Data from on-off current measurement White noise 2.3 fa/ Hz Uncertainty 0.16 ppm in 21 hours (combined type A & B uncertainty) Cable noise ULCA noise σ I / aa 10 2 Talk by F. Hohls (We-1 Quantum Standards III on Wednesday 10:30) 10 1 10 2 10 3 10 4 10 5 8 τ / s

Commercial 3 GΩ Variant ULCA-1 Available from http://www.magnicon.com/metrology/ Delivered in solid transport box with diverse accessory parts (100 MΩ, filter, divider, data logger) Includes PTB calibration certificate Single-channel variant Dual-channel variant Battery box 9

Second ULCA Generation The second ULCA generation addresses the following issues: Improved accuracy at high currents 780 MΩ ULCA with ±50nA range, 0.02 ppm uncertainty 4.7 fa/ Hz Secondary standard for ULCA gain calibrations ( CCC replacement ) High-accuracy ampere realization for currents below the QHE/CCC range Improved noise at low currents 12 GΩ ULCA with ±3.6 na range, < 0.1 ppm uncertainty 1.3 fa/ Hz 60 GΩ ULCA with ±0.5 na range, 1 ppm uncertainty 0.7 fa/ Hz Reduced measurement time / lower uncertainty Minimum noise and input bias current at ultralow currents 175 GΩ ULCA with ±5 pa range, 10 ppm uncertainty 0.43 fa/ Hz 10 aa uncertainty in 17 minutes, < 100 aa input bias current Optimized for applications that do not allow current reversal or on/off switching 10

Improved Direct Current Standard 10-1 Current range < 50 µa Relative uncertainty (k = 2) 10-2 10-3 10-4 10-5 10-6 CMCs: Capacitor charging CMCs: Calibrator and shunt, voltage drop across shunt ULCA: quarterly cal. timely cal. Two different ULCAs applied 12 GΩ & 780 MΩ Below 50 pa: ULCA cascade A TR = 1000 100 MΩ = 100 GΩ Above 50 na: Extended mode Reduced uncertainties compared to present CMCs of PTB 10-7 1f 10f 100f 1p 10p 100p 1n 10n 100n 1µ 10µ 100µ 1m 10m Performs better than 3 GΩ ULCA Current (A) 11

Low-Bias ULCA: Input Bias Stability 26 T ( C) 24 22 (a) I B,eff (aa) 0-20 -40 (b) τ = 1 h 0 1 2 3 4 5 6 7 8 9 t (d) No noticeable correlation between I B,eff and T at 10 aa level True attoampere performance 12

Low-Bias ULCA: Settling 100 G dyn (ppm) 80 60 40 20 G dyn (ppm) 4 2 0-2 -4 4 8 12 16 20 t - t 0 (s) ±50 aa 0-20 0 4 8 12 16 20 t - t 0 (s) ±5 pa test current generated via 10 GΩ resistor Output settles to within ±5 ppm or ±50 aa after 4 s 13

Low-Bias ULCA: Cable Noise Measurements 10 2 Cu-PVC coax & St-MgO coax @ 55 mk S I (fa/ Hz) 10 1 10 0 White noise 0.44 fa/ Hz 10-1 10-5 10-4 10-3 10-2 10-1 10 0 10 1 f (Hz) 10 4 Cu-PVC coax & St-MgO coax @ 55 mk σ I (aa) 10 3 10 2 10 1 White noise 0.44 fa/ Hz 10-1 10 0 10 1 10 2 10 3 10 4 10 5 τ (s) Cable combination mounted in dilution fridge with pulse tube Total noise 0.44 fa/ Hz @ 55 mk Poster Tu-P19 by C. Krause (Tuesday 14:00-15:00) 14

Conclusions ULCA optimized for characterization of SET devices 100 pa with 0.1 ppm uncertainty in 7 hours (two 12 GΩ ULCAs) Well suited for highly-accurate, traceable current measurement & generation and for resistance calibration Improved solution for applications with direct currents below 50 µa Non-cryogenic and easy-to-use instrument with excellent long-term stability Sets new accuracy benchmarks in small-current regime Improves state-of-the-art by up to two orders of magnitude 3 GΩ ULCA commercially available, 2nd generation scheduled for early 2017 http://www.magnicon.com/metrology/ More information: Drung et al., Rev. Sci. Instrum. 86, 024703 (2015) Drung et al., IEEE Trans. Instrum. Meas. 64, 3021 (2015) Drung et al., Metrologia 52, 756 (2015) Stein et al., Appl. Phys. Lett. 107, 103501 (2015) 15