CONCEPT OF DETERMINISTIC ION IMPLANTATION AT THE NANOSCALE

Transcription

1 CONCEPT OF DETERMINISTIC ION IMPLANTATION AT THE NANOSCALE Daniel Spemann Jan Meijer 1, Jürgen W. Gerlach, Paul Räcke 1, Susann Liedtke, Stephan Rauschenbach 2, Bernd Rauschenbach 1 University of Leipzig, Nuclear Solid State Physics, Leipzig 2 Max-Planck-Institute for Solid State Research, Stuttgart

2 Outline 2 Outline Motivation Why single ion implantation? Why deterministic ion implantation? State of the art of deterministic ion implantation Concepts of single ion detection: Pros and Cons Concept of the new single ion implanter Main components Ion detection using image charge Concept and first simulations of single ion detector Summary and outlook

3 Motivation Why single ion implantation? 3 Exact placement of single atoms is a key to quantum technology Example 1: magnetic sensing using nitrogen-vacancy centres in diamond Isotopically clean sample Sensitivity down to single spins can be achieved C. Degen et al., Nature Nanotechnol. 3 (2008) 643 G. Balasubramanian et al., Nature Mater. 8 (2009) 383

4 Motivation Why single ion implantation? 4 Example 2: single photon emitters, e.g. for quantum communication and cryptography First electrically driven NV single photon source A. Lohrmann et al., APL 99 (2011)

5 Motivation Why deterministic ion implantation? 5 5 kv single ion implanter at the Leibniz Joint Lab Single Ion Implantation : SPECS IQE12/38 gas ion source with ExB filter Einzel lens for focussing the ion beam into a hollow Si 3 N 4 AFM tip with nano-sized hole J. Meijer et al., Appl. Phys. A 91 (2008) 567 Ion implantation with nanometre precision, but number of ions dictated by Poisson statistics

6 Motivation Why deterministic ion implantation? 6 Number of ions is subject to Poisson statistics for timed implantation: Maximum probability of success in implanting one single ion is 36.8% Successfully implanting a chain or array of single ions is very improbable n p % % % Even chains or arrays of a few single implanted atoms, e.g. for quantum communication and processing, can only be produced via deterministic implantation of counted single ions

7 State of the art of deterministic ion implantation 7 Concepts of ion detection: Pros and cons Detection of secondary electron emission from sample upon ion impact T. Matsukawa et al., Appl. Surf. Sci. 117/118 (1997) 677 T. Shinada et al., Nature 437 (2005) 1128 Detection of charge induced in the sample from single ion hit D.N. Jamieson et al., Appl. Phys. Lett. 86 (2005) J. van Donkelaar et al., J. Phys.: Condens. Matter 27 (2015) Pro: Cons: Detection does not depend on how the ion is delivered to the implant site, e.g. masks or AFM tips can be used Sample needs to be a good SE emitter or efficient detector Detection signal must be well above noise ( unclear signals unacceptable) Single ion source based on Paul ion trap J. Meijer et al., Appl. Phys. A 83 (2006) 321 W. Schnitzler et al., Phys. Rev. Lett. 102 (2009) Pro: Cons: Detection does not depend on sample properties (can, e.g. be isolators) Substantial experimental effort and limitations on ion type Ion extraction slow (~1Hz) implantation might be spoiled by thermal drift

8 Concept of the new single ion implanter 8 The new single ion implanter in Leipzig: Main components Commercial Focused Ion Beam system with single ion source FIB: Source: Pros: Con: Raith ionline with ~3 nm beam spot size for low currents Sample stage laser-interferometer controlled to 1 nm positioning resolution Gas ion source (Electron Beam Ion Source (EBIS)) with ExB filter Collimator to match acceptance of FIB column Single ion detector that controls beam blanker in FIB column Ion detection does not depend on sample properties Acceptance of ion only for proper detection signal Ion detection must not affect the very low source emittance Funding: SAW-2025-IOM-1 Sensorik mit einzelnen Atomen

9 Concept of the new single ion implanter 9 Ion detection using image charge Demands: Concept: Emittance (beam diameter angular spread) needs to remain very small Detection and decision on acceptance of ion within ~ 1 µs Image charge detection with linear electrode array Charge detection mass spectrometry (CDMS): 22 tubes (10 mm x 5 mm, 1 pf per tube) in two sets with 11 tubes each, separated by grounded tubes Raw output from 11 tubes during passage of a macro-ion with 2500 e Image charge detected with preamplifier based on Amptek A250, 2 MHz sampling Frequency (m/z) and amplitude (q) determined using autocorrelation RMS noise ~ 10 e, detection limit ~ 100 e Smith et al., Anal. Chem. 83 (2011) 950

10 Concept of the new single ion implanter 10 Ion detection using image charge Demands: Concept: Emittance (beam diameter angular spread) needs to remain very small Detection and decision on acceptance of ion within ~ 1 µs Image charge detection with linear electrode array Charge detection mass spectrometry (CDMS): Improved setup with one tube in a cone trap, LN2 cooled JFET and FFT signal analysis Detection limit ~7 e (80% efficiency) after ~6000 cycles (~400 ms trapping time) Schematic of CDMS with cone trap and FFT analysis Keifer et al., Anal. Chem. 87 (2015) Pierson et al., J. Am. Soc. Mass Spectrom 26 (2015) 1213

11 Concept of the new single ion implanter 11 Concept of single ion detector: linear electrode array for image charge sensing Two substrates with two sets of interdigitating metallic electrodes each for image charge collection Substrates aligned on top of each other with 100 µm spacing Image charge sensed during one single fly-by of the ion Patent pending on single ion detector

12 Concept of the new single ion implanter 12 Simulation and optimization of electrode array in cooperation with Ferdinand- Braun-Institut für Höchstfrequenztechnik (Berlin): Electrodes should be arranged in small groups to reduce capacity Each group connected to a fast LN2 cooled transistor followed by a low-noise differential amplifier Feed amplified signal into filter (f, f) or lock-in amplifier Example: 670 µm period of electrodes, ion velocity v = m/s (e.g. 2.9 kev P + ) f = 200 MHz, duration of signal t ~ 1 µs, f ~ 1 MHz Velocity of ions can be set to a desired value frequency of signal is known Time of ion passage needs to be determined with ~1 µs response time Detection efficiency can be lower than 100%, but false positives must be avoided!

13 Concept of the new single ion implanter CST-Simulation of array (FBI): 13 Simulation of lock-in detection: Split array in 4 parts for lock-in and combining C = 0.24 pf R = 0.10 Ohm L = 0.44 nh Z 0 = 50 Ohm 5.31 nv Thermal noise when combining 67 arrays: U N 4kTB R 0 Nges s R Z0 Z 1 sl sc At LN2 temperature an SNR ~ 3 can be achieved nv ions Add time-shifted signals (combining): At threshold 1050: 46% detected, 54% missed, but no false positives!

14 Concept of the new single ion implanter 14 Schematic setup of deterministic ion implanter:

15 Summary and outlook 15 Summary Single ion implantation Versatile tool to manufacture devices with single atom functionality Readily available as timed implantation subject to Poisson statistics Chains or arrays of atoms require deterministic ion implantation Ion detection still a great challenge, all concepts have pros and cons Single ion implanter under construction in Leipzig FIB system will be equipped with EBIS ion source Ion detection by image charge sensing during fly-by First optimization of electrode array completed

16 Summary and outlook 16 Outlook Next steps in the near future: Integration and test of EBIS Development of ultra-low noise amplifier setups Simulation and optimization of image charge detector and data processing routines to evaluate the expected performance

17 Acknowledgements 17 Acknowledgements Ferdinand-Braun-Institut: Wolfgang Heinrich Franz-Josef Schmückle Funding: Leibniz Association (SAW-2015-IOM-1) Volkswagen-Stiftung European Union