EP4732339A1 - Quantum dot structure unit cell, quantum dot system and method of manufacturing the same - Google Patents

Quantum dot structure unit cell, quantum dot system and method of manufacturing the same

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Publication number
EP4732339A1
EP4732339A1 EP24736121.5A EP24736121A EP4732339A1 EP 4732339 A1 EP4732339 A1 EP 4732339A1 EP 24736121 A EP24736121 A EP 24736121A EP 4732339 A1 EP4732339 A1 EP 4732339A1
Authority
EP
European Patent Office
Prior art keywords
quantum dot
electrode
barrier
plunger
unit cell
Prior art date
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Pending
Application number
EP24736121.5A
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German (de)
French (fr)
Inventor
Alberto Tosato
Giordano SCAPPUCCI
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Technische Universiteit Delft
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Technische Universiteit Delft
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Publication date
Application filed by Technische Universiteit Delft filed Critical Technische Universiteit Delft
Publication of EP4732339A1 publication Critical patent/EP4732339A1/en
Pending legal-status Critical Current

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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D64/00—Electrodes of devices having potential barriers
    • H10D64/20—Electrodes characterised by their shapes, relative sizes or dispositions 
    • H10D64/27—Electrodes not carrying the current to be rectified, amplified, oscillated or switched, e.g. gates
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D48/00—Individual devices not covered by groups H10D1/00 - H10D44/00
    • H10D48/383—Quantum effect devices, e.g. of devices using quantum reflection, diffraction or interference effects
    • H10D48/3835—Semiconductor qubit devices comprising a plurality of quantum mechanically interacting semiconductor quantum dots, e.g. Loss-DiVincenzo spin qubits
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D62/00—Semiconductor bodies, or regions thereof, of devices having potential barriers
    • H10D62/80—Semiconductor bodies, or regions thereof, of devices having potential barriers characterised by the materials
    • H10D62/81—Semiconductor bodies, or regions thereof, of devices having potential barriers characterised by the materials of structures exhibiting quantum-confinement effects, e.g. single quantum wells; of structures having periodic or quasi-periodic potential variation
    • H10D62/812—Single quantum well structures
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D62/00—Semiconductor bodies, or regions thereof, of devices having potential barriers
    • H10D62/80—Semiconductor bodies, or regions thereof, of devices having potential barriers characterised by the materials
    • H10D62/82—Heterojunctions
    • H10D62/822—Heterojunctions comprising only Group IV materials heterojunctions, e.g. Si/Ge heterojunctions

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Abstract

Quantum dot structure unit cell, quantum dot system and method of manufacturing the same An quantum dot structure unit cell (1) is provided herein that comprises a substrate provided with one or more semiconducting layers, a plunger electrode structure (11P1, 11P2, 11P3), a sensing structure, barrier electrode structure (10B1, 12B1, 12B12, 12B23) and a screening electrode structure (14S). The plunger electrode structure comprises plunger electrode substructures each having a respective plunger electrode (11P1, 11P2, 11P3) to define a respective quantum dot in a respective quantum dot region (10Q1, 10Q2, 10Q3) within an active zone (1C) of the quantum dot structure unit cell. The sensing structure comprises an ohmic contact (14S) in a contact region (IOS) within the active zone (1C) to measure the conductance and/or impedance to the first quantum dot. The barrier electrode structure provides for a controllable tunnel coupling between mutually neighboring quantum dots as well as between the ohmic contact and one of the quantum dots. The screening electrode structure comprises a screening electrode (13S) at a boundary between the active zone (1C) and a routing zone (IP) surrounding the active zone.

Description

Title: Quantum dot structure unit cell, quantum dot system and method of manufacturing the same
Technical field
The present invention pertains to a quantum dot structure unit cell.
The present invention further pertains to a quantum dot system comprising a plurality of quantum dot structure unit cells in an array.
The present invention still further pertains to a method of manufacturing a quantum dot structure unit cell.
Semiconductor based qubits in electrostatically confined quantum dots constitute a promising platform for quantum information processing. Nevertheless, a practical semiconductor based quantum computer will require millions of qubits, whereas current implementations are limited to small qubit arrays. Scaling to large qubit systems has not yet been achieved due to the complexity in fabricating and controlling such systems. Random variability in the semiconductor material and in the gate-stack fabrication processes are amongst the major challenges hindering developments in this field. The need for a minimal qubit device that allows for large scale characterization of quantum dots and qubit properties across a chip, has therefore become increasingly important. Such a device would be the ideal quantum probe to provide statistical metrics for improving the heterogenous material stack constituting a qubit device, as well as the fabrication quality, and would also enable the development of robust automated quantum dots and qubits tuning and calibrating algorithms (both deterministic and Al based). SUMMARY
The present invention aims to provide means that renders it possible to obtain vast amounts of statistical data suitable to provide feedback for improving material and fabrication quality and/or for developing automated tuning and calibrating algorithms.
According to a first aspect a quantum dot structure unit cell is provided that comprises a substrate provided with a semiconducting structure suitable for forming therein hole and/or electron quantum dots.
The quantum dot structure unit cell further comprises a plunger electrode structure, a barrier electrode structure, a screening electrode structure and a sensing electrode structure.
The plunger electrode structure comprises plunger electrode substructures each having a respective plunger electrode to define a respective one of the quantum dots in a respective quantum dot region within an active zone of the quantum dot structure unit cell.
The sensing structure comprises an ohmic contact in a contact region within the active zone to measure the conductance and/or impedance of the first quantum dot (charge sensor).
The barrier electrode structure comprises a first barrier electrode substructure having a barrier electrode in a barrier region between the ohmic contact region and the quantum dot region of the first quantum dot, a second barrier electrode substructure having a barrier electrode in a barrier region between the quantum dot regions of the first and the second quantum dot and a third barrier electrode substructure having a barrier electrode in a barrier region between the quantum dot regions of the second and the third quantum dot.
The screening electrode structure comprises a screening electrode at a boundary between the active zone and a routing zone surrounding the active zone.
The quantum dot structure unit cell as defined arranged in a quantum dot structure array of arbitrary scale can be individually addressed with a control signal to the plunger electrode of the first quantum dot and a second control signal to the barrier electrode in the barrier region between the contact region and a quantum dot region of the first quantum dot. Because the active zone is bounded by the screening electrode and the potential landscape within the active zone that defines the quantum dots and their mutual tunnel couplings as well as the tunnel coupling with the ohmic contact can be accurately controlled with the plunger, barrier and screening electrode control signals.
In some embodiments overlap of barrier electrode structure elements and plunger electrode structure elements within the active zone is avoided to further improve an accuracy with which the potential landscape can be controlled.
In an embodiment of the quantum dot structure unit cell the screening electrode has extending portions in the active zone to screen electrically conducting lines to the plunger electrodes. Therewith the potential landscape in the quantum dot structure can be even more accurately controlled.
In an embodiment, the sensing structure is provided in a patterned electrically conductive layer closest to the quantum dot structure. In this embodiment a via connection to the sensing electrode is avoided. This significantly facilitates the manufacturing process. In an example thereof, the ohmic contact in the contact region in a Ge/SiGe, Si/SiGe, SiGe/Ge, Si on insulator, Ge on insulator substrate, Si or Ge substrate, is formed as a silicide, a germanide or germanosilicide at an interface of the sensing structure with the quantum dot structure in the contact region. Therewith the ohmic contact can be efficiently achieved by thermal-annealing and thus diffusing into the substrate the sensing electrode structure in the contact region. Given the superconducting properties of PtSiGe, PtGe and PtSi it is expected that such a superconducting contact may also represent an avenue for coherently coupling spin qubits of different unit cells for example by means of cross Andreev reflection coupling. It may alternatively be contemplated to provide the ohmic contact as a superconducting contact using a superconducting interconnection through a via to a superconducting line in a layer more remote from the semiconductor layers. This would however introduce an interface which generally is a source of disorder. Furthermore it would complicate the manufacturing process. It is noted that a single ohmic contact per unit cell suffices. Therewith the impedance of the first quantum dot can be measured using radio-frequency (RF) reflectometry. In some embodiments wherein the sensing electrode structure comprises a further ohmic contact in a further contact region at the opposite side of the quantum dot region of the first quantum dot. In this case the first barrier electrode substructure comprises a further barrier electrode in a barrier region between the further contact region and the quantum dot region of the first quantum dot. In these embodiments the conductance of the quantum dot can also be determined by dividing the current by the applied voltage across the quantum dot.
In an embodiment of the quantum dot structure unit cell the barrier electrode substructures each comprise a respective barrier electrode line that is electrically connected to a respective one of the barrier electrodes and that extends from a first lateral side of the unit cell to a second lateral side of the unit cell opposite the first lateral side and the plunger electrode substructures each comprise a respective plunger electrode line that is electrically connected to a respective one of the plunger electrodes and that extends from a third lateral side of the unit cell to a fourth lateral side of the unit cell opposite the third lateral side, the third and the fourth lateral side each being different from the first and the second lateral side.
This facilitates the composition of a quantum dot array at arbitrary scales by interconnecting the barrier electrode lines in a first direction, e.g. column direction, of the array and interconnecting the plunger electrode lines in a second direction of the array transverse to the first direction, in this example the row direction. An individual unit cell can be addressed by its unique pair of a plunger electrode line and barrier electrode line. In an example thereof an electrode line has a meandering trajectory that once traverses the active zone and a portion of the electrode line within the active zone serves as an electrode. Optionally the portion of the electrode line within the active zone is widened to increase its effect on the potential landscape,
In this way all electrode substructures of an electrode structure can be provided in a mutually insulated manner in a common metallization layer. If the barrier electrode structure is arranged in this manner, then the plunger electrode structure can be provided as at least substantially linear substructures spaced from each other, and therewith also mutually insulated. Likewise, if the plunger electrode structure is arranged in this manner, then the barrier electrode structure can be provided as at least substantially linear substructures spaced from each other, and therewith also mutually insulated. In an embodiment a plunger electrode line has a widened portion in the active zone forming the corresponding plunger electrode.
According to a second aspect a quantum dot system is provided that comprises a plurality of quantum dot structure unit cells arranged in a two- dimensional array and further comprises a controller.
The two-dimensional array has a first and a second mutually different array direction. Without losing generality it is presumed that the first direction is the row direction and that the second direction is the column direction.
Quantum dot structure unit cells arranged in a same row have a respective shared set of plunger electrode lines including a first shared plunger electrode line for the plunger electrode of the first quantum dot.
Quantum dot structure unit cells arranged in a same column have a respective shared set of barrier electrode lines including a first shared barrier electrode line for the barrier electrode in the barrier region between the contact region and the quantum dot region of the first quantum dot.
The controller is configured to select one of the plurality of quantum dot structure unit cells by providing a plunger electrode control signal to a selected one of the first shared plunger electrode lines line and a barrier electrode control signal to a selected one of the first shared barrier electrode lines and to read a charge state of the first quantum dot of the selected one of the plurality of quantum dot structure unit cells. It suffices that the controller has a respective plunger electrode control output for each row and a respective barrier electrode control output for each column. Therewith the quantum dot structure unit cells can be individually addressed for measuring the impedance or conductance of the sensor, which is to provide information on the charge state of the other quantum dots of the selected unit cell. The second and the third plunger electrode substructures of all quantum dot structure unit cells can each be controlled by one respective shared plunger electrode control output. Also the second and the third barrier electrode substructures of all quantum dot structure unit cells can each be controlled by one respective shared barrier electrode control output. Hence in this embodiment the number of barrier electrode connections between the controller and the quantum dot structure array can be restricted to m+2, wherein m is a number of columns in the array and the number of plunger electrode connections between the controller and the quantum dot structure array can be restricted to n+2, wherein n is the number of rows. Further a single screening electrode control line would be required and one or two connections for the sensing structure depending on the embodiment. Hence the total number of electrical connections is only proportional to the square root of the number of quantum dot structure unit cells. That is, if the number of columns is equal to the number of rows, an array with a number of nA2 unit cells comprises 2n + 6 electric connections, which includes a common electrical connection to all ohmic contacts for sensing and a common electrical connection for applying a signal to the screening electrode.
In other embodiments, the controller has a respective triplet of plunger electrode control outputs for each row and a respective triplet of barrier electrode control output for each column. Therewith a finer potential control and more complicated quantum operations in the quantum dot structure array are possible, while the total number of electrical connections is still only proportional to the square root of the number of quantum dot structure unit cells.
In other embodiments, the controller has a separate control output line for each barrier gate and plunger gate.
In other embodiments, the controller has separate DC and RF outputs. With the DC output connected as in one of the previous embodiments, and RF output connected as in one of the previous embodiments.
In another embodiment, the controller has separate DC and RF outputs.
With the DC output connected as in one of the previous embodiments, and a single RF output connected to the screening electrode or to one or more plunger or barrier electrodes. According to a third aspect a method of manufacturing a quantum dot structure unit cell is provided. The method comprises the following steps.
Providing a substrate with a quantum dot structure suitable for forming therein a first quantum dot and a pair of a second quantum dot and a third quantum dot in respective quantum dot regions within an active zone, the quantum dot structure comprising one or more semiconductor layers.
Forming a first patterned metallization layer on the semiconductor structure to form a sensing structure comprising an ohmic contact in a contact region within the active zone of the quantum dot structure.
Forming a first dielectric layer.
Forming a second patterned metallization layer to form a screening electrode structure that comprises a screening gate that bounds the active zone of the unit cell from a routing zone of the unit cell.
Forming a second dielectric layer.
Forming a third patterned metallization layer to form a barrier electrode structure comprising a first barrier electrode substructure having a barrier electrode in a barrier region between the contact region and the quantum dot region of the first quantum dot, a second barrier electrode substructure having a barrier electrode in a barrier region between the quantum dot regions of the first and the second quantum dot and a third barrier electrode substructure having a barrier electrode in a barrier region between the quantum dot regions of the second and the third quantum dot.
Forming a third dielectric layer.
Forming a fourth patterned metallization layer to form a plunger electrode structure that comprises for each quantum dot a respective plunger electrode substructure with a plunger electrode to define a quantum dot in a quantum dot region during operation.
From the description of the method it is apparent that embodiments of the quantum dot structure unit cell according to the first aspect can be manufactured with a only a minimum of four patterning and deposition steps while obviating the need for vias. The third and the fourth patterned metallization layer may be provided in a reverse order implying that the plunger electrode structure is formed before the barrier electrode structure. It is however important that the screening electrode structure is formed before forming the plunger electrode structure and the barrier electrode structure. Therewith the screening electrode structure being interposed between the quantum dot structure and the plunger electrode structure and the barrier electrode structure can more efficiently mitigate stray effects. Within the active zone the screening electrode structure may also have extensions below portions of the plunger electrode lines and around the plunger electrodes to better define the quantum dot areas.
An embodiment of the method comprises performing an annealing step in the at least one contact region of the first patterned metallization layer, therewith forming an alloy at the interface thereof with the at least one semiconductor layer and forming the ohmic contact.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other aspects of the present disclosure are described in more detail with reference to the drawings. Therein:
FIG.l schematically shows a first embodiment of a quantum dot structure unit cell according to the first aspect;
FIG. 2 schematically shows a second embodiment of a quantum dot structure unit cell according to the first aspect;
FIG. 3 schematically shows a third embodiment of a quantum dot structure unit cell according to the first aspect;
FIG. 4 schematically shows a first embodiment of a quantum dot system according to the second aspect;
FIG. 5 schematically shows a second embodiment of a quantum dot system according to the second aspect;
FIG. 6 schematically shows a fourth embodiment of a quantum dot structure unit cell according to the first aspect; FIG. 7 schematically shows a fifth embodiment of a quantum dot structure unit cell according to the first aspect;
FIG. 8 is a cross-section VIII-VIII indicated in FIG. 1 for illustrating a method of manufacturing according to the third aspect
FIG. 9 illustrates how a potential landscape is controlled in the quantum dot structure for measurement purposes;
FIG. 10 shows a practical layout of an integrated circuit comprising a quantum dot structure array;
FIG. 10A shows a portion of the quantum dot structure array of FIG. 10, FIG. 10B is a AFM-picture of said portion;
FIG. 11, 11A, 11B schematically show a sixth embodiment of a quantum dot structure unit cell according to the first aspect; Therein FIG. 11 shows an overview of the unit cell, while FIG. 11A shows the active zone thereof in more detail, and FIG. 11B shows a portion of the active zone of FIG. 11A in still further detail;
FIG. 12, 12A, 12B schematically show a seventh embodiment of a quantum dot structure unit cell according to the first aspect; Therein FIG. 12 shows an overview of the unit cell, while FIG. 12A shows the active zone thereof in more detail, and FIG. 12B shows a portion of the active zone of FIG. 12A in still further detail.
DETAILED DESCRIPTION OF EMBODIMENTS
FIG.l schematically shows a quantum dot structure unit cell 1. The unit cell 1 comprises a quantum dot structure on a substrate suitable to form therein quantum dots during operation. Particular suitable silicon- and germanium- based semiconductor quantum dot platforms include silicon-compatible quantum dot structures including silicon-germanium heterostructures, silicon metal-oxide- semiconductor (SiMOS) structures and germanium metal-oxi de- semiconductor structures. Examples of such structures are described in the article by Lawrie et al, Quantum Dot Arrays in Silicon and Germanium, Appl. Phys. Lett. 116, 080501 (2020), which is hereby incorporated by reference into this application.
For example, in an embodiment, a semiconductor layer stack on a Silicon substrate may include an intrinsic Silicon layer, an isotopically purified Silicon (28Si) epitaxial layer and a SiCL layer.
In another embodiment, the semiconductor layer stack may include a Si/SiGe heterostructure formed on a Silicon substrate, wherein the Si/SiGe heterostructure may include a graded Sii-xGex layer and an isotopically purified Silicon (28Si) epitaxial layer between two SiGe layers.
In another embodiment, the semiconductor layer stack may include a Ge/SiGe heterostructure formed on a Silicon substrate, wherein the Ge/SiGe heterostructure includes a Germanium layer followed by a reversed graded Sii- xGex and a Ge epitaxial layer between two SiGe layers.
In another embodiment, the semiconductor layer stack may include a Ge/SiGe heterostructure formed on a Ge substrate, wherein the Ge/SiGe heterostructure includes a Germanium layer followed by a forward graded Sii- xGex and a Ge epitaxial layer between two SiGe layers. This specific heterostructure is described in the article by Stehouwer et al, Germanium wafers for strained quantum wells with low disorder, (arxiv:2305.08971), which is hereby incorporated by reference into this application.
In another embodiment, the semiconductor layer stack may include a SiGe/Ge heterostructure formed on a Ge substrate, wherein the SiGe/Ge heterostructure includes a Germanium layer followed by a tensile-strained Sil- xGex . This specific heterostructure is described in patent application XXX by Scappucci et al,
In all the embodiments above, the active Si and Ge layers of the heterostructures may be isotopically purified to be depleted of elements 29Si and 73Ge carrying nuclear spins which degrade the quantum coherence of the system. Operation of the unit cell is determined by electrode structures provided on the one or more semiconductor layers. The electrode structures include a sensing structure, a screening electrode structure, a barrier electrode structure and a plunger electrode structure.
The unit cell 1 has a unit cell area with an active zone 1C and a routing IP surrounding the active zone. The active zone is partitioned in mutually distinct regions. The mutually distinct regions comprise a first quantum dot region 10Q1 provided for defining therein a first quantum dot for sensing and a second and a third quantum dot region 10Q2, 10Q3 for defining therein a second quantum dot and a third quantum dot forming a pair having a controllable tunnel coupling. A further controllable tunnel coupling is provided between the quantum dot for sensing and the second quantum dot, and between the second and the third quantum dots.
The mutually distinct regions comprise a contact region 10S in which an ohmic contact 14S is provided to measure conductance and/or impedance of the first quantum dot. The ohmic contact 14S is part of the sensing structure. In an embodiment the sensing structure is provided directly upon the one or more semiconductor layers. In an example of this embodiment the ohmic contact 14S with the quantum dot structure is formed by a thermal annealing process in which a compound is formed in the contact region 10S. The compound to be formed is for example a silicide, germanide or germanosilicide compound, preferably platinum silicide PtSi, platinum germanide PtGe or platinum germanosilicide PtSiGe. At sufficiently low temperatures, e.g. below IK these compounds become superconducting. Such a superconducting contact may also represent an avenue for coherently coupling qubits of different unit cells for example by means of cross Andreev reflection coupling, or coupling spins via a superconducting resonator. In order to form a platinumsilicide, platinumgermanide or platinumgermanosilicide it is not necessary that the sensing structure is integrally made of platinum. In some examples the sensing structure may comprise a first layer of platinum and one or more other layers of a different electrically conducting material, e.g. aluminum, molybdenum, iridium, NbTiN. Any of these metals or alloys is also suitable for use in the other electrode structures. The various electrode structures can be insulated from each other by dielectric layers, e.g. a SiNx, SiO2 or A12O3 layers.
As shown in FIG. 1, the plurality of mutually distinct regions in the active zone 10 comprises a first barrier region 10B1 between the contact region 10SR and the first quantum dot region 10Q1 as well as a second barrier region 10B12 between the first and the second quantum dot region 10Q1, 10Q2, and a third barrier region 10B23 between the second and the third quantum dot region 10Q2, 10Q3.
The quantum dot structure unit cell 1 comprises a plunger electrode structure, a barrier electrode structure and a screening electrode structure to create the potential landscape that defines the quantum dots in the quantum dot regions and sets the tunnel couplings between quantum dots in the barrier regions. The plunger electrode structure comprises a respective plunger electrode 11P1, 11P2, 11P3 to define a quantum dot in each of the quantum dot regions 10Q1, 10Q2, 10Q3. The barrier electrode structure comprises a respective barrier electrode 12B1, 12B12,12B23 in each barrier region to control each of the tunnel couplings. The screening electrode structure comprising a screening electrode 13S at a boundary between the active zone 10 and the routing zone IP to help shaping the desired potential landscape and minimizing the effect in the active region 1C of electrical perturbation happening outside the active region 1C. In the embodiment shown in FIG. 1, the screening electrode 13S has extending portions 13S1 in the active zone 1C to screen electrically conducting lines to the plunger electrodes.
FIG. 2 schematically shows an alternative arrangement having a single ohmic contact. As shown in FIG. 2, the screening gate 13S may cover a substantial area of the active zone, therewith leaving uncovered areas between adjacent electrodes 14S-12B1, 12B1-11P1, 11P1-12B12, 12B12-11P2, 11P2-12B23 and 12B23-11P3. Also a periphery around each of the plunger electrodes is left uncovered by the screening electrode, in order not to impede their operation. Although this implementation of the screening gate 13S is only shown in this example it may be valuable also in other examples for instance for modulation doped semiconductor structures which work in depletion mode. FIG. 3 shows an embodiment of the unit cell 1 having a pair of ohmic contacts 14S, 14S’ including a second ohmic contact 14S’ in a contact region 10B1’. This embodiment allows to measure conductance of the sensor by applying a voltage bias across the first quantum dot and measuring a current or vice versa.
FIG. 4 schematically shows how a plurality of quantum dot structure unit cells may be arranged in a quantum dot structure array 150 within a quantum dot system 100. In the array the quantum dot structure unit cells lij are identified by their row number “i” and their column number “j” but otherwise may be identical e.g. Nevertheless, for research purposes, different unit cells may have different implementation details, like electrode sizes and material compositions to investigate the effect thereof on the operation of the device.
In the example shown in FIG. 4, the quantum dot structure array 150 comprises a number n of rows, extending in the direction DI and a number of m columns extending in the direction D2. It may be contemplated to extend the quantum dot structure in a third direction, i.e. as a plurality of two dimensional arrays 150, stacked in a third direction D3, orthogonal to DI, D2. Alternatively, it may be contemplated to provide the quantum dot structure unit cells in a one dimensional array, e.g. as a single column or a single row.
As shown in FIG. 4 the array 150 can be easily scaled to arbitrary dimensions by adding additional rows or columns. This is rendered possible in that corresponding barrier electrodes, e.g. the barrier electrodes 12B1 of quantum dot structure unit cells 1 in the same column “j” can be interconnected to a shared barrier electrode line, e.g. Bj,i. Likewise corresponding plunger electrodes, e.g. the plunger electrodes 11P1 of quantum dot structure unit cells 1 in the same row “i” can be interconnected to a shared plunger electrode line, e.g. Pi,i.
The quantum dot system 100 comprises a controller 160 configured to select one of the plurality of quantum dot structure unit cells.
To that end the controller comprises a plunger electrode line driver 164 that is configured to provide a plunger electrode control signal to the plunger electrode line of the row with the selected quantum dot structure unit cell 1 and a barrier electrode line driver 163 to provide a barrier electrode control signal to the barrier electrode line of the column with the selected quantum dot structure unit cell 1. The controller 160, having selected a particular unit cell, can then measure the conductance and or impedance of the selected quantum dot structure unit cell. To that end the controller 160 includes a conductance and/or impedance measurement module 162. For example, in this case, wherein the quantum dot structure unit cells 1 have a single ohmic contact, e.g. as shown in FIG. 1 or 2, the impedance measurement module 162 is configured to measure the impedance of the selected quantum dot structure unit cell 1 by RF- reflectometry. Alternatively, the quantum dot structure unit cells 1 are provided in an embodiment with a pair of ohmic contacts, as shown in FIG. 3. This renders possible other methods of measuring a conductance and/or impedance, e.g. by applying a voltage bias and measuring a current or vice versa.
In some examples the controller is configured to simultaneously select a subset of two or more unit cells. For example the controller is configured to simultaneously select two or more unit cells in a same column by providing a barrier electrode control signal to the barrier electrode line of that column and to provide a plunger electrode control signal to the plunger electrode lines of two or more rows with a quantum dot structure unit cell 1 to be selected in that column. Likewise the controller may be configured to simultaneously select two or more unit cells in a same row by providing a plunger electrode control signal to the plunger electrode line of that row and to provide a barrier electrode control signal to the barrier electrode lines of two or more columns with a quantum dot structure unit cell 1 to be selected in that row.
In the embodiment shown in FIG. 4, the controller 160 has a common further barrier electrode line driver 163a with a pair of outputs for simultaneously controlling all remaining barrier electrodes 12B12 and 12B23 of the quantum dot structure unit cells 1 in the quantum dot structure array 150. One of these outputs provides the barrier electrode control signal for the barrier electrodes 12B12 and the other one provides the barrier electrode control signal for the barrier electrodes 12B23. Also, the controller 160 has a common further plunger electrode line driver 164a with a pair of outputs for simultaneously controlling all remaining plunger electrode s 11P2, 11P3 of the quantum dot structure unit cells 1 in the quantum dot structure array 150. One of these outputs provides the plunger electrode control signal for the plunger electrodes 11P2 and the other one provides the plunger electrode control signal for the plunger electrodes 11P3.
FIG. 5 shows an alternative embodiment of a quantum dot system 100 with a scalable quantum dot structure array 150. Parts therein corresponding to those of FIG. 4 have the same reference. The embodiment of FIG. 5 differs from the one of FIG. 4, in that the controller 160’ has a barrier electrode line driver 163’ with a respective triple of barrier electrode control outputs for each column. As in the embodiment of FIG. 4, one of the control outputs of the triple is configured to provide the barrier electrode control signal for controlling the barrier electrode line of the barrier electrode that controls the tunnel coupling to the ohmic contacts 14S, 14S’ of the quantum dot structure unit cells 1 in the column. The other two control outputs are configured to provide the barrier electrode control signal for controlling the barrier electrode lines of the barrier electrodes that controls the tunnel coupling between the quantum dots. In the example shown the triple of barrier electrode control outputs for the first column is configured to drive the barrier electrode lines Bi,i, BI,2, BI,3.
Also, the embodiment of FIG. 5 differs from that of FIG. 4, in that the controller 160’ has a plunger electrode line driver 164’ with a respective triple of plunger electrode control outputs for each row. As in the embodiment of FIG. 4, one of the outputs of the triple is configured to provide the plunger electrode control signal for controlling the plunger electrode line Pi,i of the plunger electrode, e.g. 11P1 of the first quantum dots 10Q of the quantum dot structure unit cells 1 in the row. The other two control outputs are configured to provide the plunger electrode control signal of the plunger electrode lines of the plunger electrodes 11P2, 11P3 of the other quantum dots. In the example shown the triple of plunger electrode control outputs for the first row is configured to drive the plunger electrode lines Pi,i, Pi, 2, Pi, 3 for the plunger electrodes 11P1, 11P2, 11P3.
In the embodiment shown in FIG. 5, it is presumed that the quantum dot structure unit cells 1 are of a type as shown in FIG. 3, having a pair of ohmic contacts 14S, 14S’ and the controller 160 comprises an alternative conductance measurement module 162’ configured to perform conductance and/or impedance of the first quantum dot by. Alternatively, the controller 160 may comprise an impedance measurement module only 162 as shown in FIG. 4. In that case it needs only a connection to one of the ohmic contacts. The other ohmic contact is superfluous, so that also the embodiment using a unit cell as shown in FIG. 1 or 2 is suitable.
As shown in the examples of FIGs. 1-3, each of the electrode structures can be provided in a single metallization layer, while avoiding that electrode lines of mutually different electrodes in the electrode structure contact each other. For example, it can be seen that the plunger electrode structure comprises a first, a second and a third plunger electrode 11P1, 11P2, 11P3 each having a proper plunger electrode line Pi,i, P2, P3 and its connection thereto. The plunger electrode 11P1 is connected to a branch of the plunger electrode line Pi,i. Likewise the plunger electrode 11P3 is connected to a branch of the plunger electrode line P3. The plunger electrode 11P2, which is arranged between the plunger electrodes 11P1 and 11P3 is electrically connected to the plunger electrode line P2 in that it is integral therewith. As can be seen in Figures 1,2 and 3, the plunger electrode line P2 has a meandering trajectory that once crosses the active zone 1C, and has a portion, here a widened portion, within the active zone forming the plunger electrode 11P2. As shown in FIGs. 1-3 therewith it is avoided that plunger electrode line P2 crosses the branch to plunger electrode P13.
As shown in FIG. 6, in this way the unit cell can be easily extended to define a number of quantum dots larger than 3. In this example the unit cell has two additional quantum dots each defined by an additional plunger electrode. As in the examples of FIGs. 1-3 the plunger electrode lines P2, P3, P4, of the plunger electrodes 11P2, 11P3, 11P4 each have a meandering trajectory that once crosses the active zone 1C. In this example a portion within the active zone forming the corresponding plunger electrode 11P2, 11P3, 11P4 is widened. Therewith an arbitrary number of mutually insulated plunger electrode substructures can be provided in a single metallization layer. In the example shown, the unit cell 1 comprises a pair of ohmic contacts 14S1, 14S2, which are coupled to a respective line Oa, Ob to enable conductance measurements. In an alternative version of the unit cell of FIG. 6 only a single ohmic contact is provided enabling RF-based impedance measurements.
FIG. 7 shows another example, wherein the same principle is applied to the barrier electrode lines B2, B3, B4 for the barrier electrodes 12B12, 12B23 and 12B45. These barrier electrode lines B2, B3, B4 each have a meandering trajectory that once crosses the active zone 10, and of which a portion within the active zone forms the corresponding barrier electrodes 12B12, 12B23 and 12B45. In this example shown, the unit cell 1 comprises a single ohmic contact 14S coupled to a line 0 for the purpose of enabling RF-based impedance measurements. In an alternative version a pair of ohmic contacts coupled to a respective line Oa, Ob is provided to enable conductance measurements.
An embodiment of a method of manufacturing an improved unit cell is now described with reference to FIG. 8 which is a cross-section VIII-VIII indicated in FIG. 1.
The method comprises providing a substrate SBS, e.g. a Si-substrate or a Ge-substrate which comprises one or more semiconductor layers suitable for the formation of electron and/or hole quantum dots in quantum dot regions 10Q1 thereof. Particular suitable silicon based semiconductor quantum dot platforms include silicon-compatible quantum dot structures including silicon-germanium heterostructures and silicon metal-oxide-semiconductor (SiMOS) structures.
Examples of such structures are described in the article by Lawrie et al, Quantum Dot Arrays in Silicon and Germanium, Appl. Phys. Lett. 116, 080501 (2020), which is hereby incorporated by reference into this application.
For example, in an embodiment, a semiconductor layer stack on a Silicon substrate may include an intrinsic Silicon layer, an isotopically purified Silicon (28Si) epitaxial layer and a SiO2 layer.
In another embodiment, the semiconductor layer stack may include a Si/SiGe heterostructure formed on a Silicon substrate, wherein the Si/SiGe heterostructure may include a graded Si(l-x)Gex layer and an isotopically purified Silicon (28Si) epitaxial layer between two SiGe layers. In another embodiment, the semiconductor layer stack may include a Ge/SiGe heterostructure formed on a Silicon substrate, wherein the Ge/SiGe heterostructure includes a Germanium layer followed by a reversed graded Sil- xGex and a Ge epitaxial layer between two SiGe layers.
In another embodiment, the semiconductor layer stack may include a Ge/SiGe heterostructure formed on a Germanium substrate, wherein the Ge/SiGe heterostructure includes a Germanium layer followed by a forward graded Sii- xGex and a Ge epitaxial layer between two SiGe layers.
In another embodiment, the semiconductor layer stack may include a Ge/SiGe heterojunction formed on a Germanium substrate, wherein the Ge/SiGe heterostructure includes a Germanium layer followed by a Sii-xGex layer.
In the previous embodiments both Ge and Si can be purified to e.g. 28Si and 70Ge, to reduce the amount of nuclear spins.
As a further step a first patterned metallization layer Ml is formed on the semiconductor structure to form a sensing structure comprising an ohmic contact 14S in a contact region of the semiconductor structure.
A first dielectric layer II is then deposited. Upon the first dielectric layer a second patterned metallization layer M2 is formed which provides a screening electrode structure comprising a screening electrode 13S surrounding a active zone 1C of the unit cell comprising the quantum dot regions and the contact region.
Then a second dielectric layer 12 is deposited (or the top part of the metallization layer is oxidized to form a dielectric) followed by forming a third patterned metallization layer M3 that provides a barrier electrode structure comprising barrier electrodes for controlling tunnel couplings within the active zone.
Subsequently a third dielectric layer 13 is deposited (or the top part of the metallization layer is oxidized to form a dielectric), followed by a fourth patterned metallization layer M4 to form a plunger electrode structure that comprises a respective plunger electrode to define a quantum dot in each quantum dot region. The screening electrode structure, the plunger electrode structure and the barrier electrode structure together define the potential landscape during operation of the device. Alternatively the plunger electrode structure may be formed before forming the barrier electrode structure. It is important however that forming the screening electrode structure precedes forming the plunger electrode structure and forming the barrier electrode structure, to effectively screen the electric field generated by the plungers and/or barriers electrodes where desired. Less effective, but also possible is an embodiment wherein the screening electrode structure is arranged between the barrier electrode structure and the plunger electrode structure. It is further preferred that the first metallization layer that defines the sensing structure is formed directly upon the semiconductor structure. In this way ohmic contacts with the first quantum dot can be efficiently achieved by performing an annealing step in a contact region of the first patterned metallization layer with the surface of the semiconductor structure. In this step an alloy is formed between the metal of the first patterned metallization layer and the material of the semiconductor structure. For example in case the metallization layer Ml comprises platinum a platinum silicide PtSi, a platinum germanosilicide PtSiGe or a platinum germanide PtGe is formed depending on the nature of the semiconductor structure. The alloys are superconducting at sufficiently low temperatures. It may alternatively be contemplated to provide the ohmic contact as a superconducting contact using a superconducting interconnection through a via to a superconducting line in a layer more remote from the semiconductor stack. This would however introduce an interface which generally is source of disorder. Furthermore it would complicate the manufacturing process.
The upper part of FIG. 9 shows a portion of the quantum dot structure unit cell 1 of FIG. 3. The lower part of FIG. 9 shows a potential landscape along the direction DI in an operational state. As shown therein the plunger electrode 11P1, 11P2 and 11P3 locally define a low potential in this operational state so that a respective quantum dot Ql, Q2, Q3 is formed in the corresponding quantum dot regions. The barrier electrode 12B12 provides for a controllable tunnel coupling between the quantum dots Ql, Q2 and the barrier electrode 12B23 provides for a controllable tunnel coupling between the quantum dots Q2, Q3.
Quantum operations can be performed by applying an RF signal to one or more of the electrodes in the active zone after the potential landscape has been defined by the DC control signals to the electrodes.
Each quantum dot structure unit cell 1 in a quantum dot system 100 can be sensed independently from the others by simultaneously setting a potential to the barrier electrode 12B1 and a potential to the plunger electrode 11P1, such that it is energetically favorable for charge carriers to accumulate under the plunger electrode and there is a sufficient tunnel coupling to the ohmic contact (or contacts if two) to measure conductance and/or impedance. In case the quantum dot system 100 comprises a barrier electrode line driver 163’ with separate outputs for controlling each barrier electrode line in each column of quantum dot structure unit cells 1 and comprises a plunger electrode driver 164’ with separate control outputs for controlling each plunger electrode line in each row of quantum dot structure unit cells 1 it is possible to define a mutually different potential landscapes in the quantum dot structure unit cells 1.
In summary, the present disclosure provides for a virtually arbitrarily scalable quantum dot system 100 wherein the quantum dot structure unit cells can be individually controlled and sensed. This renders it possible to obtain vast amounts of statistical data serving to provide feedback about the semiconductor material, the manufacturing process and quality of the electrode stack. The statistical data may comprise one or more of:
• threshold turn-on and pinch-off voltages of the tunnel coupling with the ohmic contact
• charging energy of each dot
• lever arm of each electrode
• charge stability diagrams and the electrode voltages associated to each charge state
• g-factor
• spin orbit
• resonance frequency of qubits • characteristic coherence dephasing times
• readout fidelity
• charge noise
• gate fidelity
• quality factor and other common metrics used for characterizing qubits.
In an embodiment, the quantum dot system 100 is used to generate datasets to train machine learning algorithms and/or to develop and test deterministic algorithm for tuning and operating spin qubits.
FIG. 10 shows a practical layout for an integrated circuit 1000 comprising a quantum dot structure array 150 with 23 x 23 quantum dot structure unit cells 1, each having a surface area of lxl pm2. The total number of plunger electrode lines comprising a set, e.g. SP1, of three lines for each row is 69. Also the total number of barrier lines comprising a set, e.g. SB1, of three lines for each column is 69. In addition the quantum dot structure array 150 has a pair of ohmic lines Oa, Ob and a screening electrode control line SG. The screening electrode control line is connectable at two sides. It can be seen in FIG. 10, that the fan out of the plunger electrode lines to plunger electrode line contacts comprises a first portion of plunger electrode line sets SPl,...,SPn/2 at the right hand side of the integrated circuit 1000 and a second portion of plunger electrode line sets SPn/2+l,...,SPn at the left hand side of the integrated circuit 1000. Likewise, the fan out of the barrier lines to barrier line contacts comprises a first portion of barrier line sets SBl,...,SBn/2 at the top side of the integrated circuit 1000 and a second portion of barrier line sets SBn/2+l,...,SBn at the bottom side of the integrated circuit 1000. This renders possible a smaller footprint of the integrated circuit 1000.
FIG. 10A shows a portion of the quantum dot structure array 150 comprising 3x3 quantum dot structure unit cells 1.
FIG. 10B is a AFM-picture of a portion of the array 150 with an area of 2x2 pm2, the boundary of 1 unit cell 1 is indicated therein. The AFM-picture further shows the height variation of the surface of about 100 nm. FIG. 11, 11A and 11B schematically shows a sixth embodiment of a quantum dot structure unit cell according to the first aspect. As best visible in FIG. 11A, in the embodiment of FIG. 11 the active zone 1C of the unit cell 1 is provided with a two-dimensional matrix of data quantum dot regions wherein data quantum dots are formed during operation by a control voltage provided to respective plunger electrodes 11P21,...,1P51,...11P24„. 11P54. Also a first and a second measurement quantum dot are formed during operation in respective further quantum dot regions by a control voltage provided to the plunger electrodes 11P1 and 11P6. A proper ohmic contact 14S1, 14S2 is provided with which an RF impedance measurement can be performed. The ohmic contacts 14S1, 14S2 are tunnel coupled to the quantum dots formed in the regions defined by the plunger electrodes 11P1, 11P6 respectively by a barrier electrode 12B1 connected to barrier electrode line Bi and by a barrier electrode 12B7 connected to barrier electrode line B? respectively. It is noted that alternatively conductance measurements may be performed by a pair of ohmic contacts arranged at mutually opposite sides of a further quantum dot region.
As shown in further detail in FIG. 11B a tunnel coupling between adjacent data quantum dot regions in a same row is determined by a portion of a barrier electrode line that extends between the adjacent regions. In the plane of the drawing a quantum dot Qij in a quantum dot region defined by plunger electrode HPij may be tunnel coupled to a quantum dot in a quantum dot region on the left side wherein the strength of the tunnel coupling is controllable by a control voltage applied to the barrier electrode line Bi of which a portion forms the barrier electrode 12Bi-l, i. By way of example the quantum dot Qij in the quantum dot region defined by plunger electrode HPij is the one next to the quantum dot in the quantum dot region defined by plunger electrode 11P1. Likewise, in the plane of the drawing the quantum dot Qij may be tunnel coupled to the quantum dot in a quantum dot region on the right side, wherein the strength of the tunnel coupling is controllable by a control voltage applied to the barrier electrode line Bi+i of which a portion forms the barrier electrode 12Bi, i+1.
As further shown in FIG. 11, 11A and 11B, and best visible in FIG. 11B, a tunnel coupling between adjacent data quantum dot regions in a same column is determined by a pair of barrier electrode 12Bi, 12Bi+l. A first one 12Bi thereof is formed by a branch of the barrier electrode line Bi on the left (in the plane of the drawing) and the other one 12Bi+l thereof is formed by a branch of the barrier electrode line Bi+i on the right. The arrangement shown in FIG. 11, 11A and 11B, renders it possible to independently enable the tunnel coupling between quantum dots in a same row at mutually opposite sides of a barrier electrode line by providing a proper control voltage to a selected one of the barrier electrode lines. Due to the fact that the proper control voltage for enabling tunnel coupling is provided to only one branch of the pair of branches between quantum dots that are mutually adjacent in the direction of the column the tunnel coupling between these adjacent quantum dots remains disabled. On the other hand if a relatively modest control voltage is applied to barrier electrode lines Bi, Bi+i on both sides of a column of quantum dots, the pair of branches enables a tunnel coupling between mutually adjacent quantum dots in a column, while tunnel coupling between quantum dots that are mutually adjacent in a row is disabled. The selectivity for independently controlling the tunnel coupling in the row direction and in the column direction can be further tuned by the width of the barrier electrode control lines relative to their branches. In the embodiment shown in FIG. 11B the barrier electrode lines are wider than their branches.
FIG. 12, 12A and 12B schematically show a seventh embodiment of a quantum dot structure unit cell according to the first aspect. As in the embodiment of FIG. 11, the active zone 1C of the unit cell 1 is provided with a two-dimensional matrix of data quantum dot regions wherein data quantum dots are formed during operation by a control voltage provided to respective plunger electrodes 11P21,...,1P51,...11P24„. 11P54. In this embodiment the unit cell 1 comprises a pair of barrier electrode structures provided in mutually different metallization layers. Preferably the metallization layers of the barrier electrode structures are arranged between the metallization layer of the plunger electrodes structure and the metallization layer of the sensing structure. The mutual order of the barrier electrode structures is however not important. The first barrier electrode structure comprises a first set of respective barrier electrode lines Bai, Ba2,...Ba7 to respective column barrier electrode elements to control a tunnel coupling between quantum dots of a same row in mutually adjacent columns. The second barrier electrode structure comprises a second set of respective barrier electrode lines Bbi, Bb2,...Bb5 to respective row barrier electrode elements to control a tunnel coupling between quantum dots of a same column in mutually adjacent rows. In the embodiment shown, the first set of barrier electrode lines comprises two additional barrier electrode lines Bai, Ba? as compared to the second set to control a tunnel coupling with the first ohmic contact 14S1, and a tunnel coupling with the second ohmic contact 14S2. In this embodiment, a single ohmic contact 14S1, 14S2 is provided at each side to perform RF based measurements. Alternatively conductance based measurements may be performed by a pair of ohmic contacts arranged at mutually opposite sides of a further quantum dot region.
FIG. 12B shows in further detail a portion of the active zone 10 centered around a quantum dot Qij formed during operation by a control voltage applied to plunger electrode 1 lPij. A controllable tunnel coupling is provided with adjacent quantum dots in the same row and with adjacent quantum dots in the same column. The tunnel coupling with a quantum dot on the left side of the quantum dot Qij is controlled by the voltage on the barrier electrode 12Bai applied to barrier electrode line Bai. The quantum dot on the left side is for example a data quantum dot formed in same row, in the column on the left of that of the quantum dot Qij. Furthermore, the barrier electrode voltage on the barrier electrode line Ba2 controls the tunnel coupling between the measurement quantum dot (charge sensor) defined by plunger electrode 11P1 and the data quantum dot defined by plunger electrode 11P21. The barrier electrode voltage on the barrier electrode line Ba? controls the tunnel coupling between the measurement quantum dot defined by plunger electrode P6 and the data quantum dot defined plunger electrode 11P54.
The tunnel coupling between mutually adjacent quantum dots in the same column is controlled by the control voltage on barrier electrode lines of the second set. In the example of FIG. 12B a tunnel coupling with a quantum dot above the quantum dot Qij is controlled by the voltage on the barrier electrode 12Bbj applied to barrier electrode line Bbi and a tunnel coupling with a quantum dot below the quantum dot Qij is controlled by the voltage on the barrier electrode 12Bbj+l applied to barrier electrode line Bbi+i.
Whereas FIG. 11 and FIG. 12 show an example wherein the active zone comprises two-dimensional matrix with 4 rows and 4 columns, other embodiments may be conceived with smaller or larger number of rows, and/or with a smaller or larger number of columns.

Claims

1. A quantum dot structure unit cell (1) comprising: a substrate (SBS) provided with a semiconducting structure suitable for forming therein a first, a second and a third hole and/or electron quantum dot in respective quantum dot regions (10Q1, 10Q2, 10Q3) within an active zone (1C) of the quantum dot structure unit cell, a plunger electrode structure that comprises a respective plunger electrode substructure, having a respective plunger electrode (11P1, 11P2, 11P3) to define a respective one of the quantum dots, and a respective plunger electrode line (Pj,l, P2, P3) that is electrically connected to the respective plunger electrode; a sensing structure comprising an ohmic contact (14S) in a contact region (10S) and a line (0) coupled to the ohmic contact, to perform charge sensing to the first quantum dot; a barrier electrode structure comprising a first barrier electrode substructure having a first barrier electrode line (Bi,l) and a first barrier electrode (12B1) in a barrier region (10B1) between the contact region (IOS) and the quantum dot region (10Q1) of the first quantum dot and that is electrically connected to the first barrier electrode line, a second barrier electrode substructure having a second barrier electrode line (B2) and a second barrier electrode (12B12) in a barrier region (10B12) between the quantum dot regions (10Q1, 10Q2) of the first and the second quantum dot and that is electrically connected to the second barrier electrode line and a third barrier electrode substructure having a third barrier electrode line (Bi,l) and a third barrier electrode (12B23) in a barrier region (10B23) between the quantum dot regions (10Q2, 10Q3) of the second and the third quantum dot, characterized in that the unit cell further comprises a screening electrode structure comprising a screening electrode (13S) at a boundary between the active zone (1C) and a routing zone (IP) surrounding the active zone, the contact region (IOS) of the ohmic contact (14S) is within the active zone and in that the first, the second and the third barrier electrode line (Bi,l, B2, B3) each extend from a first lateral side (LA) of the unit cell to a second lateral side (LB) of the unit cell opposite the first lateral side, the plunger electrode lines (Pj,l, P2, P3) each extend from a third lateral side (LC) of the unit cell to a fourth lateral side (LD) of the unit cell opposite the third lateral side, the third and the fourth lateral side each being different from the first and the second lateral side.
2. The quantum dot structure unit cell (1) of claim 1 wherein the screening electrode (13S) has extending portions (13S1) in the active zone (1C) to screen electrically conducting lines to the plunger electrodes (11P1, 11P2, 11P3) and/or covers a substantial area of the active zone.
3. The quantum dot structure unit cell (1) according to claim 1, wherein the sensing structure is provided in a patterned electrically conductive layer (ML1) closest to the quantum dot structure (SL).
4. The quantum dot structure unit cell (1) according to claim 3, wherein the ohmic contact in the contact region is formed as a silicide, a germanide or germanosilicide at an interface of the sensing structure with the quantum dot structure in the contact region (IOS).
5. The quantum dot structure unit cell (1) of claim 1, wherein an electrode line has a meandering trajectory that once traverses the active zone (1C).
6. The quantum dot structure unit cell (1) of any of the preceding claims, wherein the electrode line is a plunger electrode line having a widened portion in the active zone (1C) forming the corresponding plunger electrode (11P2).
7. The quantum dot structure unit cell (1) of any of the preceding claims wherein the active zone (1C) of the unit cell (1) is provided with a two- dimensional matrix of data quantum dot regions.
8. The quantum dot structure unit cell (1) according to claim 7, wherein tunnel coupling between adjacent data quantum dot regions in a same column is determined by a pair of a first barrier electrode (12Bi) formed by a branch of a barrier electrode line (Bi) at a first side of the column and a second barrier electrode (12Bi+l) that is formed by a branch of the barrier electrode line (Bi+1) at a second side of the column opposite the first side.
9. The quantum dot structure unit cell (1) according to claim 8, wherein a width of the barrier electrode lines differs from a width of the branches thereof.
10. The quantum dot structure unit cell (1) according to claim 7 comprising a pair of a first barrier electrode structure and a second barrier electrode structure, wherein the first barrier electrode structure comprises a first set of respective barrier electrode lines (Bal, Ba2,...Ba7) to respective column barrier electrode elements to control a tunnel coupling between quantum dots of a same row in mutually adjacent columns, and wherein the second barrier electrode structure comprises a second set of respective barrier electrode lines (Bbl, Bb2,...Bb5) to respective row barrier electrode elements to control a tunnel coupling between quantum dots of a same column in mutually adjacent rows.
11. A quantum dot system (100) comprising: a plurality of quantum dot structure unit cells (111, 121, ...,11m, lnm) according to claim 1 arranged in a two-dimensional array (150) with a first and a second mutually different array direction (DI, D2), wherein respective first sets of quantum dot structure unit cells are arranged along the first direction (DI) have a respective shared set (SP1, SP2,...,SPn) of plunger electrode lines including a first shared plunger electrode line (Pl,l, P2,l, ...,Pn,l) for the plunger electrode (110P1) of the first quantum dot of the quantum dot structure unit cells arranged along the first direction; and wherein respective second sets of quantum dot structure unit cells arranged along the second direction (D2) have a respective shared set of barrier electrode lines (SB1,. SB2, SBm) including a first shared barrier electrode line (Bl,l, B2,l, ...,Bm,l) for the barrier electrode (12B1) in the barrier region (10B1) between the contact region (10S) and the quantum dot region (10Q1) of the first quantum dot; a controller (160) configured to select one of the plurality of quantum dot structure unit cells by providing a plunger electrode control signal to a selected one of the first shared plunger electrode lines line (Pl,l, P2,l, ...,Pn,l) and a barrier electrode control signal to a selected one of the first shared barrier electrode lines (Bl,l, B2,l, ...,Bm,l) and to measure the conductance or/and impedance of the first quantum dot (the charge sensor) which provides information on the charge state of the quantum dots in the unit cell.
12. The quantum dot system according to claim 11, wherein the two- dimensional array (150) is provided as an integrated circuit wherein a first number of shared sets (SPl,...,SPn/2) of plunger electrode lines and a second number of shared sets (SPn/2+l,...,SPn) of plunger electrode lines have a fanout at respective mutually opposite first and second sides of the integrated circuit and wherein a first number of shared sets (SBl,...,SBn/2) of barrier electrode lines and a second number of shared sets (SBn/2+l,...,SBn) of barrier electrode lines have a fanout at respective mutually opposite third and fourth sides of the integrated circuit, the first and second sides each being different from each of the third and fourth sides.
13. A method of manufacturing a quantum dot structure unit cell (1) as specified in claim 1, comprising: providing a substrate (SBS) with a semiconducting structure suitable for forming therein a first, a second and a third hole and/or electron quantum dot within an active zone (1C), the substrate comprising one or more semiconductor layers (SL); depositing a first patterned metallization layer (Ml) on the semiconductor structure to form a sensing structure comprising a contact (14S) in a contact region (IOS) within the active zone of the quantum dot structure and a line (0) coupled to the contact; depositing a first dielectric layer (II); depositing a second patterned metallization layer (M2) to form a screening electrode structure that comprises a screening electrode (13S) bounding the active zone (1C) of the unit cell from a routing zone (IP) of the unit cell (1); depositing a second dielectric layer (12); depositing a third patterned metallization layer (M3) to form a barrier electrode structure comprising a first barrier electrode substructure having a first barrier electrode line (Bi,l) and a first barrier electrode (12B1) in a barrier region (10B1) between the contact region (IOS) and the quantum dot region (10Q1) of the first quantum dot and that is electrically connected to the first barrier electrode line, a second barrier electrode substructure having a second barrier electrode line (B2) and a second barrier electrode (12B12) in a barrier region (10B12) between the quantum dot regions (10Q1, 10Q2) of the first and the second quantum dot and that is electrically connected to the second barrier electrode line and a third barrier electrode substructure having a third barrier electrode line (Bi,l) and a third barrier electrode (12B23) in a barrier region (10B23) between the quantum dot regions (10Q2, 10Q3) of the second and the third quantum dot; depositing a third dielectric layer (13); depositing a fourth patterned metallization layer (M4) to form a plunger electrode structure that comprises for each quantum dot a respective plunger electrode substructure with a respective plunger electrode in a respective plunger electrode region overlapping the quantum dot region of the quantum dot and a respective plunger electrode line that is electrically connected to the respective plunger electrode, wherein the first, the second and the third barrier electrode line (Bi,l, B2, B3) each extend from a first lateral side (LA) of the unit cell to a second lateral side (LB) of the unit cell opposite the first lateral side, the plunger electrode lines (Pj, 1, P2, P3) each extend from a third lateral side (LC) of the unit cell to a fourth lateral side (LD) of the unit cell opposite the third lateral side, the third and the fourth lateral side each being different from the first and the second lateral side.
14. The method of claim 13, comprising performing an annealing step of the first patterned metallization layer (sensing layer) to create ohmic contacts, therewith forming an alloy at the interface thereof with the at least one semiconductor layer and forming the ohmic contact.
15. The method of claim 13 or 14, comprising performing an etching step before depositing the first metallization layer in the ohmic contact region.
EP24736121.5A 2023-06-22 2024-06-21 Quantum dot structure unit cell, quantum dot system and method of manufacturing the same Pending EP4732339A1 (en)

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