High Temperature Resistant ReRAM

Advantages

• This is a resistive random access memory element that can tolerate temperatures of over 300°C, and it can be applied to memory integrated circuits that operate in extreme environments and neuromorphic computer elements used in AI hardware.
• We have confirmed that the memory function is maintained for long periods of time, even in high-temperature environments and that its characteristics are maintained stably.
• Using a 4-terminal element, we implemented a type of associative learning called Pavlovian conditioning and confirmed that it is possible to mimic higher-order neural functions using this invention.
• It is possible to stack the device structure in multiple layers without selecting the base substrate.

Technology Overview & Background

In fields such as automobiles, aerospace and the IoT, ReRAM is attracting attention as a next-generation memory element that can operate stably even in harsh environments. In particular, ReRAM that uses metal oxides shows non-volatile resistance changes due to the movement of oxygen vacancies and oxygen ions inside the device, and active research and development is being carried out due to the simplicity of its structure and low power consumption. Until now, the main focus of research has been on “filament-type” ReRAM, which uses materials such as titanium oxide, tantalum oxide, and hafnium oxide, and in which the resistance changes as the filaments that show conductivity when voltage is applied are connected. However, while the filament-type can achieve a high resistance ratio, there is still room for improvement in terms of performance variation and long-term reliability, as the position and size of the filaments cannot be controlled.

These researchers have succeeded in developing a new “non-filamentary-type” ReRAM. Specifically, the researchers verified the functionality of a non-filamentary-type ReRAM by using a capacitor-type ReRAM with an amorphous gallium oxide film between the electrodes, and confirmed that it functions as a non-filamentary-type ReRAM in which the distribution state of oxygen vacancies changes. In addition, it was demonstrated that this functionality is maintained stably even in high-temperature environments of 300°C or higher, and that the memory function can be maintained for long periods of time.

This technology also makes it possible to mimic the structure and function of biological neural synapses, which are higher-order neural functions. In biological synapses, plasticity is regulated by synaptic connections with interneurons and neuromodulators (heterosynaptic plasticity), and we have experimentally confirmed that this technology can be used in combination with a four-terminal element to artificially mimic the same function (details below).

Furthermore, this technology is also suitable for 3D integrated circuits because it allows the device structure to be stacked in multiple layers without selecting the substrate as a base. In addition to memory integrated circuits that operate in extreme environments such as high temperatures, aerospace, and radiation, it is expected to be used in brain-type computer elements used in AI hardware.

Data

• We used the pulsed laser deposition method to create gallium oxide, also known as a wide bandgap semiconductor, as a reduced amorphous thin film with a thickness of several tens of nanometers, and then created a capacitor-type ReRAM by sandwiching it between an upper electrode (Pt) and a lower electrode (ITO).

When the current-voltage characteristics were measured, a “reverse figure-of-eight hysteresis characteristic” was obtained, in which the output current changes in response to the application of positive/negative voltage to the upper electrode, and it was found that it has a memory function. Furthermore, it was confirmed that the resistance change was stable even at high temperatures of 600K (see figure on the right). In addition, titanium oxide as well as gallium oxide, which is resistant to high temperatures, can mimic higher-order biological neural functions by using oxygen vacancy distribution type resistance change characteristics. By setting the presence or absence of a “conditioned response” based on the high or low electrical conductivity between the T1-T3 terminals, it was confirmed that the electrical conductivity gradually increased by periodically repeating the simultaneous application of a voltage equivalent to food (unconditioned stimulus) and a voltage equivalent to a bell (conditioned stimulus). Furthermore, once the electrical conductivity had reached a high value due to the simultaneous application of voltage, it remained high even with only the application of the voltage corresponding to the bell. From these results, it was confirmed that it was possible to artificially mimic the elements corresponding to the conditioned response.

Publication(s)

Sato K., et al., Sci Rep 13, 1261 (2023).
[DOI]  https://doi.org/10.1038/s41598-023-28075-4

Ikeuchi T., et al., Appl. Phys. Express 16, 015509 (2023).
[DOI]   https://doi.org/10.35848/1882-0786/acb0ae

Miyake R., et al., ACS Appl. Electron. Mater. 4, 2326 (2022).
[DOI]  https://doi.org/10.1021/acsaelm.2c00161

Patent(s)

JP 7591784 (B1)

Researchers & Academic Institution

Akira Sakai, PhD (Professor, Graduate School of Engineering Science, Osaka University, Japan)

Expectations

TECH MANAGE is now looking for companies to collaborate with the researcher(s) and develop this technology further under the licensing of the related patent(s) described above.
You can also consider joint research using the invention, providing know-how under a confidentiality agreement (CDA), or setting up evaluation or licensing options for a certain period.

Project No.JT-03195