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Dynamic electromechanical control of semiconductor nanostructures by acoustic fields

Periodic Reporting for period 2 - SAWTrain (Dynamic electromechanical control of semiconductor nanostructures by acoustic fields)

Reporting period: 2017-06-01 to 2019-05-31

The dynamic modulation of semiconductor structures using vibrations in the form of surface acoustic waves (SAWs) provides a powerful tool for the control of the materials properties required for novel functionalities in the ‘More than Moore’ pathway to integrated devices. SAWs are elastic vibrations propagating on a solid surface: their fields modulate the material properties and create moving potentials for the transport of carriers. SAWs with (sub) micron wavelengths can be electrically generated on a piezoelectric by interdigital transducers (IDTs) fabricated using planar semiconductor technology. SAWs on piezoelectric insulators are used for numerous applications, most notably in signal processing, sensors and acousto-optics, where they have a well-established place. Acoustic devices incorporated in millions of mobile phones attest to the economic and societal impact of the technology.

The network consists of 10 leading European groups (including 9 universities or research centres and a private sector laboratory) and 15 associated partners (APs). Its main goal is to establish an interdisciplinary and innovative training network (ITN) for 15 early stage researchers (ESRs) at the PhD level to explore the novel functionalities provided by SAWs.

While supporting conventional application areas, the network will mainly focus on the exploitation of SAWs for the control of carriers, spins and photons as well as chemical reactions in semiconductors and related structures. Interestingly, most of the scientific and technological breakthroughs in this field have been made since the late 1990’s by beneficiaries of this consortium. These led to novel SAW-based functionalities for signal processing, sensors, optical modulators and switches, nano-mechanical structures, and quantum control of single electrons, photons, and phonons, which are key enabling technologies with high societal impact. Research will address (i) advanced materials and technologies for SAWs, integration with Si-CMOS, and applications in (ii) advanced sensors and (iii) chemical control; (iv) advanced nanoelectromechanics, tunable and integrated photonic devices; (v) SAW-mediated flying qubits transfer between quantum dots; (vi) SAW-induced light storage, spin transport, and single-photon sources; and (vii) the manipulation of single SAW quanta by superconducting qubits.

A further goal of the network is to increase the visibility of the field and enable innovation by strengthening the bridge between basic research and applications. The formation of human resources combined with extensive outreach, dissemination, and exploitation activities will setup a long-term platform for basic studies and applications of acoustics, thereby consolidating European leadership in the area.

The action concluded on May 31st 2019.
The SAWtrain members joined their efforts to provide training through research in three main research areas: phononics, photonics, and electronics organized in three work packages (WPs). Phononics was mainly addressed in WP1, which addressed materials and processing technologies for the generation of high-frequency SAWs on novel materials and their integration with the CMOS technology. This WP also investigated novel concepts for SAW-based sensing elements and for the acoustic control of chemical reactions. In addition, WP1 provided the technological basis for WP2 and WP3. WP2 combined photonics and phononics activities: here, it exploited acoustic and optic resonators for the control of SAW and light quanta down to the single-particle level. WP3 was devoted to electronic functionalities related to the transport and manipulation of charge and spin by moving SAW fields. Emphasis was placed on carrier and spin control at the single-particle level for application in quantum information processing, supported by theoretical contributions.

In all scientific work packages ESRs conducted cutting edge research activities. Scientific highlights in each work package include:
WP1: Simulation and fabrication of interdigitated transducers (IDTs) via nano-imprint lithography (NIL) on CMOS compatible substrates
WP2: Demonstration of the non-exponential decay of a giant superconducting artificial atom
WP3: Design, fabrication and measurement of electronic SAW devices for single-electron transport in a beam-splitter configuration with transfer efficiencies exceeding 99%.

At the time the final report was submitted, ESRs of the network had published 24 peer-reviewed articles, 11 Research Highlights and 1 book chapter. Several of these works appeared in high-impact journals including Nature Physics, Physical Review X and Nature Communications.

SAWtrain PIs were guest editors of a special issue of the Journal of Physics D “Surface Acoustic Waves in Semiconductor Nanosystems” (https://iopscience.iop.org/journal/0022-3727/page/Special-Issue-on-Surface-Acoustic-Waves-in-Semiconductor-Nanosystems) with 25 contributions.

The special issue was concluded by the “2019 surface acoustic wave roadmap” (https://iopscience.iop.org/article/10.1088/1361-6463/ab1b04). In 15 contributions more than 35 authors shared their opinions on the hot topics of SAW research in the coming years; ranging from quantum technologies, advanced device concepts to biotechnologies on a chip with SAWs.
The network hired 15 fellows for the 10 beneficiaries of the action, incorporated in PhD programs of leading universities in Europe. It also implemented an organizational infrastructure to manage the training, dissemination and exploitation activities of the network supported by an advisor board.

The originality and innovative aspects of the research program relied on the complementary expertise and infrastructures from institutions from both the academic (universities and research institutes) and non-academic (e.g. industrial) sectors. The structured ESR PhD program was carried out under co-mentorship in these institutions and accompanied by complementary training in transferable skills. Examples were given by training in presentation skills, dissemination, IP and patenting. Here, social impact arose from capacity building in technical and personal skills as well as the transformation of knowledge into products and services. The special training conditions offered by SAWtrain raised the career perspectives of the fellows far beyond those of current programs, therefore enhancing their career prospects and employability. In this way, the fellows are able to fully exploit their potential and have outstanding career perspectives.

The multidisciplinary basic research addressing physical mechanisms, material properties, and technological processes increased knowledge and led to new materials and functionalities for acoustic devices, as well as in their exploitation for products and services. These activities led to several contributions to specialized journals, conferences, and schools. Here, the network was very active in increasing the visibility of the field via the organization of several symposia, workshops, and specialized schools in the field of physics and applications of high frequency vibrations.

The SAWtrain project has designed and built an easily portable hardware demonstrator with a protective carrying case for use in public outreach events. 11 final versions of the demonstrator have been made, one of which has been sent to each beneficiary, and one to the Deutsches Museum in Munich.
Overview of the SAWtrain scientific workpackages (cycles) illustrating the interactions between bene