EP-4453938-B1 - SUPERCONDUCTING BIPOLAR THERMOELECTRIC MEMORY AND METHOD FOR WRITING A SUPERCONDUCTING BIPOLAR THERMOELECTRIC MEMORY

Inventors

• GIAZOTTO, Francesco
• PAOLUCCI, Federico
• BRAGGIO, Alessandro
• MARCHEGIANI, Giampiero
• GERMANESE, Gaia

Dates

Publication Date

20260513

Application Date

20221220

Claims (4)

1. Superconducting bipolar thermoelectric memory (1) comprising: - a bipolar thermoelectric junction (2) and a predetermined resistive load (4) electrically connected in parallel, and - a current generator (6) configured to inject a current (I b ) in the bipolar thermoelectric junction (2) and the predetermined resistive load (4), wherein - the bipolar thermoelectric junction (2) is arranged to be heated by a predetermined thermal gradient and to generate corresponding output voltages (V L + , V L - ) on the resistive load (4) depending on the sign of the injected current (I b ), these output voltages (V L + , V L - ) corresponding to respective logic states (0, 1) stored by the supercondcuting bipolar thermoelectric memory (1); and - the bipolar thermoelectric junction including a semiconductor layer (22) put in contact with a superconductor layer (24) which is configured to act as a cold electrode of the superconducting bipolar thermoelectric memory (1), the semiconductor layer (22) having an energy gap Eg comparable with the energy gap 2Δs of the superconductor layer (24) implying that the ratio 2Δs/Eg is in the range between 0.3 - 0.7 and the bipolar thermoelectric junction further including a metallic top gate (26) and a bottom gate (28) configured to control the energy gap of the bipolar thermoelectric junction and an oxide layer (30) placed between the semiconductor layer (22) and the top and bottom gates (26, 28).
2. Superconducting bipolar thermoelectric memory (1) according to claim 1, wherein a maximum distance between the output voltages (V L + , V L - ) decreases by increasing the predetermined thermal gradient.
3. Superconducting bipolar thermoelectric memory (1) according to any of the preceding claims. wherein the bipolar thermoelectric junction (2) and the load resistor (4) are arranged to be placed at a predetermined cryogenic temperature to ensure the superconductive state of the bipolar thermoelectric junction (2), and the current generator (6) is arranged to be placed at room temperature.
4. Method for writing a superconducting bipolar thermoelectric memory comprising the steps of: - providing (200) a superconducting bipolar thermoelectric memory (1) according to any of the preceding claims and applying a thermal gradient to the superconducting bipolar thermoelectric memory (1); - injecting (202) a current (I b ) to the bipolar thermoelectric junction (2) and the resistive load (4), thus causing the generation of the output voltage (V L ) on the resistive load (4) having a positive (V L + ) or negative (V L - ) value depending on the sign of the injected current (I b ); and - increasing or reducing the injected current (I b ) so that the output voltage (V L ) changes (204) its sign, thus changing the state of the superconducting bipolar thermoelectric memory (1).

Description

The present invention relates to a superconducting memory capable of encoding a logic state into an output electrical voltage, thanks to the presence of a finite thermal gradient representing the power supply of the memory itself (bipolar thermoelectric effect), and to a method for writing such superconducting memory. The recent quantum technologies development has led to increasing interest in the study of thermoelectric phenomena in superconducting and hybrid devices. The main reason lies in the control of thermal phenomena, which are inevitably generated in devices used in computing environments. The innovative methodologies are focused on the management of the heat generated in this kind of devices and the miniaturization of their components; they represent the main challenge in both classical and quantum computation. Moreover, the possibility to control thermoelectric phenomena generated in superconductors becomes also an asset for the development of new high-sensitivity sensors. One of the main challenges related to these technologies is recycling the heat produced in computing environments. Known superconducting memories [IEEE Trans. Appl. Supercond. 2, 95-100 (1992); Phys. Procedia 36, 35-41 (2012); IEEE Trans. Appl. Supercond. 23, 1701208-1701208 (2013); Nat. Commun. 5, 3888 (2014); Nat. Commun 6, 8628 (2015); New J. Phys. 19, 063015 (2017); Supercond. Sci. Technol. 32, 015001 (2018); Appl. Phys. Lett. 118, 112603 (2021)] do not contribute to the recycling of the heat produced in computing environments, and they have limitations in response times since they are driven by magnetic field pulses. There is therefore the need to have a superconducting memory capable of employing the heat dissipated in electrical components exploited in quantum and classical computation, with high response speed, and stable and durable performances, thus overcoming the problems of the prior art. These and other objects are fully achieved by virtue of a superconducting bipolar thermoelectric memory having the characteristics defined in independent claim 1, and by a method for writing a superconducting memory having the characteristics defined in claim 4. Preferred embodiments of the invention are specified in the dependent claims 2 and 3. Only embodiments or examples comprising all the features of independent device claim 1 or of independent method claim 4 fall under the scope of protection of the present invention. Further characteristics and advantages of the present invention will become apparent from the following description, provided merely by way of non-limiting example, with reference to the attached drawings, in which: Figure 1 shows a schematic view of the electrical circuit of a superconducting bipolar thermoelectric memory according to the present invention;Figure 2 shows a graph of the output voltage vs. the injected current in the superconducting memory;Figure 3 shows multiple hysteretic curves of figure 2 obtained by applying raising thermal gradients;Figures 4a - 4c show a top view of junctions forming the thermoelectric element of the superconducting memory;Figure 5 shows a sectional view of a Superconductor-Insulator-Superconductor-Ferromagnetic insulator junction;Figure 6 shows a sectional view of a Superconductor-Insulator-Semiconductor junction according to the present invention;Figure 7 shows a current-voltage characteristic of the thermoelectric element; andFigure 8 shows a block diagram of the step of a method for writing a superconducting memory according to the present invention. The present invention is a superconducting memory based on the bipolar thermoelectric effect. The superconducting memory encodes two (or more) logic states into an electrical output voltage in the presence of a fixed thermal gradient, which can be determined by a direct power supply or from another source of heat (heat harvesting). The memory is volatile since, in the absence of a temperature gradient (power supply), it cannot store the output state. The superconducting bipolar thermoelectric memory of the present invention allows reconverting the heat dissipated in logic elements of a circuit into on-chip reusable electrical DC power. In particular, the superconducting memory exploits a bipolar thermoelectric effect generated in a superconducting tunnel junction in the presence of a thermal gradient (nonlinear regime) across the junction [Phys. Rev. Lett. 124, 106801 (2020); Phys. Rev. B 101, 214509 (2020); Phys. Rev. B 104, 184502 (2021)], assuming a suppressed Josephson coupling, which would be detrimental for the operation of the memory itself. An appropriate material and design selection, used for the realization of the superconducting memory, potentially permits extending its operating range to not only cryogenic temperatures. In this way, the superconducting memory becomes easier to apply. Figure 1 shows a schematic view of the electric circuit of a superconducting bipolar thermoelectric memory 1 according to the