Periodic Reporting for period 1 - STMICRO (Space-time visualization of microelectronic chip operation with femtosecond electron microscopy)
Berichtszeitraum: 2020-04-01 bis 2022-03-31
Addressed problem: Information processing by modern microelectronic circuits relies on ever-smaller and ever-faster components. The foreseen time (femtosecond) and spatial (nanometer) scales of electronic components surpass the capability of modern diagnostic tools. Thus, research and development of smaller and faster electronics, is restricted by our inability to see and measure electron dynamics in semiconductor chips at sufficient resolution in time and space. Ultimately, a novel approach is required, that would offer a superior resolution, that cannot be provided by electronics itself. A combination of laser technology and electron microscopy, called ultrafast electron microscopy, can satisfy both spatial and temporal demands. Form these fundamental considerations it follows that ultrafast electron microscopy is the enabling technology for the research and development of semiconductor chips for the years to come.
Importance for society: The EC Horizon 2020 program points out that nanoelectronic devices are the “key Enabling Technologies driving the Europe’s growth and competitiveness” and “essential building blocks in addressing societal challenges”. A novel principle for the diagnostics of fastest electronic circuits therefore has a far-reaching potential, facilitating the development of next-generation (6G and beyond) telecommunication and electronics in general.
Overall objectives: Electron microscopy and laser technology are in the Ultrafast Electron Microscope (UEM). The UEM allows to visualize atoms and electrons in motion on their natural time and length scales. Here, UEM is used to investigate fundamental electron transport and in operando diagnostics elementary microelectronic devices. The overall research objective of the proposal is to use femtosecond electron pulses to probe rapidly switching electric fields in microelectronic structures.
Conclusions of the action: A proof-of-principle method for investigation the dynamics of electrons and electromagnetic fields in microelectronic structures is demonstrated with femtosecond, micrometer and millivolt resolution (M. Volkov et al., manuscript in preparation, 2022). A platform for characterizing electron pulses interacting with terahertz transients is devised, providing sub-femtosecond time resolution (M. Volkov et al., https://doi.org/10.48550/arXiv.2206.13805(öffnet in neuem Fenster)). Further exploration of ultrafast electronics with electron microscopy tools will be continued by the fellow in the next career steps.
Importance for society: The EC Horizon 2020 program points out that nanoelectronic devices are the “key Enabling Technologies driving the Europe’s growth and competitiveness” and “essential building blocks in addressing societal challenges”. A novel principle for the diagnostics of fastest electronic circuits therefore has a far-reaching potential, facilitating the development of next-generation (6G and beyond) telecommunication and electronics in general.
Overall objectives: Electron microscopy and laser technology are in the Ultrafast Electron Microscope (UEM). The UEM allows to visualize atoms and electrons in motion on their natural time and length scales. Here, UEM is used to investigate fundamental electron transport and in operando diagnostics elementary microelectronic devices. The overall research objective of the proposal is to use femtosecond electron pulses to probe rapidly switching electric fields in microelectronic structures.
Conclusions of the action: A proof-of-principle method for investigation the dynamics of electrons and electromagnetic fields in microelectronic structures is demonstrated with femtosecond, micrometer and millivolt resolution (M. Volkov et al., manuscript in preparation, 2022). A platform for characterizing electron pulses interacting with terahertz transients is devised, providing sub-femtosecond time resolution (M. Volkov et al., https://doi.org/10.48550/arXiv.2206.13805(öffnet in neuem Fenster)). Further exploration of ultrafast electronics with electron microscopy tools will be continued by the fellow in the next career steps.
(WP1) We devised and implemented an efficient electron-terahertz velocity-matched interaction platform for 70-keV femtosecond electron bunches on a silicon prism. i) finite-difference time domain (FDTD) numerical simulations were used to calculate the optimal angle and dimensions of the silicon prism. A prism with the desired dimensions was acquired from a commercial supplier and installed in the interaction chamber of an ultrafast electron diffraction beamline. ii) The THz radiation with p-polarization was generated and delivered onto the prism, providing a streaking gradient of 400 as per camera pixel, and sub-femtosecond overall resolution. iii) a classical trajectory Monte Carlo simulation code was developed to understand the electron-terahertz velocity-matched interaction in detail and to further optimize the device. iv) we designed the Schottky diode in several variations (gold and aluminum plated) with the combined effort of the Fraunhofer Institute for Solar Energy Systems and University of Konstanz Nanolab. We deposited additional gold layers on the Schottky diode to study the effect of THz penetration depth and screening. v) we obtained the electron streaking deflectograms with and without the Schottky diode and developed a 1 kHz lock-in detection scheme for enhanced sensitivity of potential rectification features.
(WP2) The frequency limits were directly explored on integrated circuits that also have metal-semiconductor (Schottky and Ohmic) contacts. i) We devised and fabricated a printed-circuit-board microchip, driven by a picosecond photodiode. Femtosecond laser pulses were generated via bulk compression, coupled into the vacuum chamber and aligned onto the fast photodiode. Synchronized electron pulses then probe parts of the circuit in a stroboscopic manner. Here, bending of the electron beam trajectories is recorded for different time delays between the laser-triggered voltage pulses and the probing electron beam. ii) In a proof-of-principle experiment, we demonstrate the ability to measure voltage pulses on a printed circuit board via the femtosecond electron beam (fs-eBeam). Compared to a modern GHz oscilloscope, our femtosecond eBeam allows to see local voltage transients the oscilloscope cannot resolve. Further, we show that eBeam is effectively impedance free, local probe that also gives superior resolution is space without disturbing the circuit. iii) We repeat the measurements with a photoconductive switch with a femtosecond rise time. We show how the dispersion of the printed circuit board limits the maximum speed of its operation, by recording its time-dependent voltage response with a picosecond temporal resolution.
(WP3) A 4D pulsed electron oscilloscope was realized. i) we designed and fabricated a terahertz-supporting microchip. We deposit on a gallium arsenide wafer an elementary circuit with a coplanar waveguide, photoconductive switch, bias and termination contacts. We perform basic calculation showing that the microchip supports terahertz frequency of operation. ii) We mount the microchip in the vacuum chamber of the electron beamline and arrange a tightly-focused optical excitation. iii) We record the generation, propagation, dispersion and reflection of the electric field pulse with micrometer, millivolt and femtosecond accuracy, by utilizing terahertz compression of the electron pulses. We further explore the nonlinearities of the system by varying the bias potential and observe mechanisms of the electric pulse amplitude.
(WP2) The frequency limits were directly explored on integrated circuits that also have metal-semiconductor (Schottky and Ohmic) contacts. i) We devised and fabricated a printed-circuit-board microchip, driven by a picosecond photodiode. Femtosecond laser pulses were generated via bulk compression, coupled into the vacuum chamber and aligned onto the fast photodiode. Synchronized electron pulses then probe parts of the circuit in a stroboscopic manner. Here, bending of the electron beam trajectories is recorded for different time delays between the laser-triggered voltage pulses and the probing electron beam. ii) In a proof-of-principle experiment, we demonstrate the ability to measure voltage pulses on a printed circuit board via the femtosecond electron beam (fs-eBeam). Compared to a modern GHz oscilloscope, our femtosecond eBeam allows to see local voltage transients the oscilloscope cannot resolve. Further, we show that eBeam is effectively impedance free, local probe that also gives superior resolution is space without disturbing the circuit. iii) We repeat the measurements with a photoconductive switch with a femtosecond rise time. We show how the dispersion of the printed circuit board limits the maximum speed of its operation, by recording its time-dependent voltage response with a picosecond temporal resolution.
(WP3) A 4D pulsed electron oscilloscope was realized. i) we designed and fabricated a terahertz-supporting microchip. We deposit on a gallium arsenide wafer an elementary circuit with a coplanar waveguide, photoconductive switch, bias and termination contacts. We perform basic calculation showing that the microchip supports terahertz frequency of operation. ii) We mount the microchip in the vacuum chamber of the electron beamline and arrange a tightly-focused optical excitation. iii) We record the generation, propagation, dispersion and reflection of the electric field pulse with micrometer, millivolt and femtosecond accuracy, by utilizing terahertz compression of the electron pulses. We further explore the nonlinearities of the system by varying the bias potential and observe mechanisms of the electric pulse amplitude.
i) We achieve the main objective of the proposal – that is demonstration of femtosecond, micrometre and millivolt electron-beam probing of microelectronic structures in proof-of-principle experiments on realistic circuits. This result significantly advances the electron beam probing technique in terms of temporal resolution, by two orders of magnitude and the current electron beam capabilities. It therefore opens the possibility of investigating and characterizing fastest electronic circuits for the next-generation (6G and beyond) telecommunications. The achieved resolution in time, space and voltage allows to identify small fabrication defects in terahertz circuits. This diagnostic principle therefore could be used in research, development and quality control of fast electronic circuits.
ii) with the help of generated terahertz pulses, we demonstrate a method of complete spatio-temporal characterization of electron pulses with record-high temporal resolution in the attosecond streaking regime. Third, based on this result, we propose a novel scheme for electron pulse compression and manipulation, accompanied with an open-source simulation code, that was developed during the fellowship. The demonstrated results are expected to trigger further research of microelectronics via ultrafast electron microscopy towards in operando diagnostics to support research and development enduring the Moore's law.
ii) with the help of generated terahertz pulses, we demonstrate a method of complete spatio-temporal characterization of electron pulses with record-high temporal resolution in the attosecond streaking regime. Third, based on this result, we propose a novel scheme for electron pulse compression and manipulation, accompanied with an open-source simulation code, that was developed during the fellowship. The demonstrated results are expected to trigger further research of microelectronics via ultrafast electron microscopy towards in operando diagnostics to support research and development enduring the Moore's law.