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Toward high operating temperature AlN-based ferroelectric random access memory

Drury, Daniel E., III
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Brennecka, Geoffrey
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2023
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Keywords
AlScN
 ferroelectric
 high temperature
 memory
 nitride
 sputter deposition
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2023 - Mines Theses & Dissertations
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https://hdl.handle.net/11124/179117
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Abstract
There is an absence of non-volatile memory technologies that can operate beyond 200 °C. The development of high operating temperature (HOT) ferroelectric random access memory (RAM) based on wurtzite nitride materials is promising for enabling data storage in extreme environments such as Venus long lander missions, jet engine monitoring, automotive applications, and geothermal exploration. Conventionally, electronic systems are designed to withstand up to 125 °C with a few platforms rated to 200 °C. When considering applications upwards of 300 °C, there is an inherent difficulty and lack of materials capable of withstanding these conditions. Thermal energy severely impacts Si-base technologies, therefore a shift toward SiC is necessary due to the larger band gap, structural stability, and inert behavior. Currently, two major challenges lie ahead for HOT electronics: non-volatile memory and packaging. In the ferroelectrics field, the discovery of a wurtzite and a nitride material in 2019 provided two unique characteristics and therefore, a novel set of material properties to study and harness. Here, the focus is on Al1−xScxN and Al1−y By N synthesis, temperature-dependent electrical properties, and the applicability and compatibility for integration with SiC-based fabrication processes as a non-volatile memory component. The first step toward this goal is to establish a reliable and repeatable thin film deposition process for AlScN and AlBN, which was accomplished by optimizing against the desired structural (c-axis texture) and electrical properties (ferroelectric switching). While these properties can be tuned with many factors, the substrate quality, substrate temperature, glow-discharge stability, and gas composition are among the most significant. Sputter deposition processes were developed to synthesize epitaxial ferroelectric AlM N/Mo/4H-SiC (M =Sc or B) heterostructures to use for high-temperature electrical characterization. Switching dynamics, fatigue effects, imprint behavior, and polarization retention are the primary performance metrics investigated between 23 and 400 °C to develop a holistic understanding of an AlN-based ferroelectric RAM. Additionally, the highest temperature ferroelectric hysteresis loops were conducted at 800 °C on an Al0.7Sc0.3N/Mo/4H-SiC stack. The materials, techniques, and perspectives developed throughout this thesis ensure further exploration and integration of AlN-based ferroelectrics in novel devices.
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