3D Vertical Ferroelectric Capacitors for Memory Scaling

3D vertical ferroelectric capacitors are revolutionizing memory technology, offering higher density and performance by leveraging vertical structures to overcome planar scaling limits. Using aluminum-doped hafnium oxide (Al:HfO₂), these capacitors achieve stable remnant charge, low voltage operation, and enhanced scalability, addressing advanced applications in AI and edge computing. Recent innovations, such as the TiN/Al:HfO₂/TiN configuration introduced by Dongguk University, South Korea, demonstrate improvements in endurance and integration. This progress builds on foundational work by Qimonda and Fraunhofer IPMS-CNT in Dresden Germany, including Tim Böscke's pioneering discovery of ferroelectricity in hafnium oxide and Johannes Müller's ALD advancements using ALD process developments FHR and ASM tools. These developments cement Al:HfO₂ as a DRAM and CMOS-compatible solution for next-generation non-volatile memory technologies.

3D vertical ferroelectric capacitors are transforming memory technology by providing higher density and performance in compact designs. Leveraging a vertical structure, they overcome planar scaling limits by using the third dimension to maximize storage capacity. Incorporating ferroelectric materials like aluminum-doped hafnium oxide (Al:HfO₂) enables these capacitors to achieve spontaneous polarization and stable remnant charge even at reduced dimensions. With features like low voltage, high-speed operation, and improved retention and endurance, they address critical challenges in advanced memory while remaining compatible with CMOS processes, facilitating their integration into existing manufacturing technologies. This innovation is key to meeting the demands of data-intensive applications such as AI and edge computing.

A recent study, 3D Vertical Ferroelectric Capacitors with Excellent Scalability (by Eunjin Lim et al Dongguk University, South Korea)), introduces a 3D vertical ferroelectric capacitor with a TiN/Al:HfO₂/TiN configuration. It employs a unique architecture with multiple small holes sharing a common pillar electrode, enhancing ferroelectric properties and scalability. Analyses using advanced microscopy confirm its structural integrity, while the device demonstrates high endurance, minimal variability, and excellent retention. This architecture also supports integration into one-transistor n-capacitor ferroelectric memory with vertical transistors.

Importantly, Earlier work by Fraunhofer IPMS-CNT, including the 2012 study Incipient Ferroelectricity in Al-Doped HfO₂ Thin Films, first demonstrated ferroelectric properties in HfO₂ thin films doped with aluminum. This research identified an antiferroelectric-to-ferroelectric phase transition, influenced by Al concentration and annealing conditions, and attributed ferroelectricity to a non-centrosymmetric orthorhombic phase (Pbc2₁). This foundational work highlighted the potential of Al:HfO₂ for applications in memory and sensing technologies.

The later paper High Endurance Strategies for Hafnium Oxide-Based Ferroelectric Field Effect Transistors further emphasized Al:HfO₂’s scalability and compatibility with CMOS technology. It explored strategies to improve endurance and reduce interfacial stress, including modifying interfacial materials and exploring MFS structures. These strategies balance performance, reliability, and scalability, supporting the broader adoption of ferroelectric memory.

In Johannes Müller's PhD thesis (2014, Fraunhofer IPMS-CNT), the Atomic Layer Deposition (ALD) processes for hafnium oxide (HfO₂) and aluminum-doped hafnium oxide (Al:HfO₂) utilized advanced deposition equipment to achieve precise doping and phase control. The processes were performed using a 300 mm FHR ALD 300 and an ASM PULSAR 3000®, both of which are designed for high-uniformity deposition on large substrates, such as 300 mm wafers. These tools facilitated the use of tetrakis(ethylmethylamino)hafnium (TEMAHf) and trimethylaluminum (TMA) as precursors for hafnium and aluminum, respectively, along with oxidants like water or ozone. By tailoring precursor ratios, deposition temperatures, and annealing conditions, the processes ensured the stabilization of the orthorhombic Pbc2₁ phase, critical for the ferroelectric properties of Al:HfO₂ films. These advancements highlight the scalability and compatibility of ALD-fabricated Al:HfO₂ films with CMOS technology.

Semiconductor Cleanroom Tools: Introducing ASM Eagle XP4 for ALD | Fraunhofer IPMS

Historic picture of the FHR ALD 300 mm tool, at the previous location of Fraunhofer IPMS-CNT. The FHR cluster was co-developed by Qimonda and Fraunhofer CNT and teh original discovery of ferroelectric hafnium oxide was by Qimonda and a PhD Student from TU Dresden, Tim Böscke. His groundbreaking work, published in 2011, demonstrated the ferroelectric properties of silicon-doped hafnium oxide (Si:HfO₂), marking a major milestone in the development of CMOS-compatible ferroelectric materials. This discovery laid the foundation for integrating ferroelectric properties into hafnium oxide-based systems, revolutionizing non-volatile memory technologies

The patent US 2009/0057737 A1, authored by Tim Böscke et al., describes a method for fabricating integrated circuits with a dielectric layer that exhibits enhanced properties, such as high dielectric constants and ferroelectricity. The process involves forming a preliminary dielectric layer, such as hafnium oxide or doped hafnium oxide (e.g., aluminum- or silicon-doped), using techniques like Atomic Layer Deposition (ALD). The dielectric layer is initially amorphous and undergoes a phase transition to a crystalline state upon heating above its crystallization temperature. The method includes precise doping of the dielectric layer to stabilize desirable phases, such as orthorhombic or tetragonal, which are essential for achieving ferroelectricity. A covering layer, often a conductive electrode material, is deposited before annealing to assist in crystallization and enhance material properties. The innovations outlined aim to improve memory applications, such as capacitors and transistors, by offering higher storage densities, lower leakage currents, and compatibility with advanced CMOS processes. This patent is foundational in the development of ferroelectric hafnium oxide-based technologies.

Sources:

• 3D Vertical Ferroelectric Capacitors with Excellent Scalability: 3D Vertical Ferroelectric Capacitors with Excellent Scalability | Nano Letters
• Mueller, S., et al., Incipient Ferroelectricity in Al‐Doped HfO₂ Thin Films, Advanced Functional Materials, 2012. Wiley Online Library
• High Endurance Strategies for Hafnium Oxide-Based Ferroelectric Field Effect Transistor, Fraunhofer IPMS, 2016. (N-432037.pdf): N-432037.pdf
  Ferroelektrizität in Hafniumdioxid und deren Anwendung in nicht-flüchtigen Halbleiterspeichern Ferroelektrizität in Hafniumdioxid und deren Anwendung in nicht-flüchtigen Halbleiterspeichern
• US 2009/0057737A1 (prev. QIMONDA AG, now NAMLAB GGMBH) https://patentimages.storage.googleapis.com/56/02/b2/d476f4848ffe82/US20090057737A1.pdf

3D Ferroelectric NAND for Ultra-High Efficiency Analog Computing-in-Memory by SK hynix

3D FeNAND with Ultra-High Computing-in-Memory Efficiency: AI models containing up to trillions of parameters require substantial memory resources to handle the vast amounts of data. Energy-efficient analog computing-in-memory (CIM) devices such as 3D vertical NAND architectures are emerging as potential solutions because they offer high areal density and are non-volatile. SK hynix researchers will detail how they achieved analog computation in ultra-high-density 3D vertical ferroelectric NAND (FeNAND) devices for the first time. They used gate stack engineering techniques to improve the analog switching properties of 3D FeNAND cells, and achieved an unprecedented ≥256-conductance-weight levels/cell. The 3D FeNAND arrays improved analog CIM density by 4,000x versus 2D arrays, and demonstrated stable multiply-accumulate (MAC) operations with high accuracy (87.8%) and 1,000x higher computing efficiency (TOPS/mm²) versus 2D arrays. This work provides an efficient method to implement the processing of hyperscale AI models in analog CIM chips for edge computing applications, where speed and low power operation are the critical requirements, not extreme accuracy.

 

Above:

(1)   is a comparison of 2D and 3D arrays for analog-CIM applications.

(2)   is a TEM analysis  of the 3D FeNAND, showing (a) a top-down view of the device; (b) a cross-sectional view at low magnification; (c) a cross-sectional view at high magnification; and (d) a schematic illustration of the FeFET cells in the 3D FeNAND array.

Source: 

IEDM 2024 Paper #38.1, “Analog Computation in Ultra-High Density 3D FeNAND for TB-Level Hyperscale AI Models,” J.-G. Lee and W.-T. Koo et all, SK hynix https://www.ieee-iedm.org/press-kit

Watch again - Material development for MRAM and FRAM stacks at Fraunhofer IPMS-CNT

Material development for MRAM and FRAM stacks

Dr. Lukas Gerlich & Konrad Seidel (Fraunhofer IPMS - Center Nanoelectronic Technologies)

Today, data is the lifeblood disrupting many industries. The vast majority of this data is stored in the form of non-volatile magnetic bits in hard disk drives. This technology was developed more than half a century ago and has reached fundamental scaling limits that prevent further increases in storage capacity. New approaches are needed.

In the webinar, FRAM (Ferroelectric Random Access Memory) and MRAM (Magnetoresistive Random Access Memory) will be presented as two promising concepts for future ultra-low power memory technologies. Special attention will be paid to material development and fabrication on state-of-the-art industrial equipment for 300 mm wafers.

Watch now: Webinars - Fraunhofer IPMS

Previous Webinar: Fe- FET - A Memory Device for Maximum Integration, Konrad Seidel (IoT Components and Systems) Webinars - Fraunhofer IPMS

Unraveling the different causes behind ferroelectricity in HfO2

Interplay between oxygen defects and dopants: effect on structure and performance of HfO2-based ferroelectrics

Monica Materano et al
Inorg. Chem. Front., 2021, Advance Article https://doi.org/10.1039/D1QI00167A

Abstract: Ten years after the first report on ferroelectricity in HfO2, researchers are still occupied unraveling the different causes behind this phenomenon. Among them, oxygen related defects seem to play a major role, affecting both crystalline phase formation and performance of HfO2-based devices. This review surveys the available literature and provides a broad picture on the topic, starting with an overview of existing oxygen-related defects, assessing the extensive calculations and experimental reports on phase stabilization in both undoped and doped HfO2 and concluding with a discussion of device reliability involving oxygen vacancies, first in more classical HfO2 applications such as MOSFET high-k metal gate and resistive switching devices and later in the three major groups of ferroelectric non-volatile memory devices.

Progress and future prospects of negative capacitance electronics: A materials perspective

NaMLab and TU Dresden, who has performed groundbreaking research on Ferroelectric hafnium oxide are also deep into Negtavie Capacitance devices for electronics to come. They have postulated 5 requirements for prospective ferroelectric materials that NC transistors need to fulfill to be useful for practical devices:

1. Robust ferroelectricity at 5 nm thickness and below
2. Compatibility with CMOS technology
3. Thermal stability on silicon
4. Conformal deposition on 3D substrates
5. Large electronic bandgap and conduction band offset to Si

Looking at the number 4 - ALD will come in handy. Enjoy the reading of their prospect paper below, which is open access.

Progress and future prospects of negative capacitance electronics: A materials perspective

Michael Hoffmann, Stefan Slesazeck, and Thomas Mikolajick

APL Materials 9, 020902 (2021); https://doi.org/10.1063/5.0032954

Negative capacitance in ferroelectric materials has been suggested as a solution to reduce the power dissipation of electronics beyond fundamental limits. The discovery of ferroelectricity and negative capacitance in the widely used class of HfO2-based materials has since sparked large research efforts to utilize these effects in ultra-low power transistors. While significant progress has been made in the basic understanding of ferroelectric negative capacitance in recent years, the development of practical devices has seen limited success so far. Here, we present a unique view of the field of negative capacitance electronics from the ferroelectric materials perspective. Starting from the basic principles of ferroelectric negative capacitance, we discuss the desirable characteristics of a negative capacitance material, concluding that HfO2-based ferroelectrics are currently most promising for applications in electronics. However, we emphasize that material non-idealities can complicate and in some cases even inhibit the design and fabrication of practical negative capacitance devices using HfO2-based ferroelectrics. Finally, we review the recent progress on experimental devices and give an outlook on the future direction of the field. In particular, further investigations of the microscopic structure of HfO2-based ferroelectrics are needed to provide an insight into the origin of negative capacitance in this material system and to enable predictive device design

Historic trend of the supply voltage Vdd and equivalent oxide thickness (EOT) scaling in commercial metal–oxide–semiconductor field-effect transistor (MOSFET) technologies. The black dashed line indicates the EOT limit given by the necessary SiO2 interface between the Si channel and the high-k material, and the red dashed lines indicates the minimum supply voltage due to the Boltzmann limit. HKMG: high-k metal gate. NC: negative capacitance.

Ferroelectric Field Effect Transistors (FeFETs) Bring Promise And Challenges

It is truly amazing to see the progress of FMC in Dresden and the recent drive in the semiconductor industry for Ferro FETs. Continuously you read about involvement from many of the big names in the industry. Here is a very good overview of the current status written by Bryon Moyer at Semiengineering.

[Article in Semiengineering]: Ferroelectric FETs (FeFETs) and memory (FeRAM) are generating high levels of interest in the research community. Based on a physical mechanism that hasn’t yet been commercially exploited, they join the other interesting new physics ideas that are in various stages of commercialization.

“FeRAM is very promising, but it’s like all promising memory technologies — it takes a while to get beyond promising,” said Rob Aitken, fellow and director of technology on the research team at Arm. “It has the potential to have better benefits than the other new non-volatile memory (NVM) technologies that are on the table today.”

Ferroelectric behaviors are opening up opportunities for non-volatile memory, combined logic/memory functions, and neuromorphic modeling. While it’s still early days for the technology, developers are cautiously optimistic about its future.

Source/Full version: LINK

CEO interview: FMC’s Pourkeramati on roadmaps, turning away investors
https://www.eenewsanalog.com/news/ceo-interview-fmcs-pourkeramati-roadmaps-turning-away-investors

The annealing and zirconium quantity have a strong impact on the crystal arrangement. Source: FMC

A comparasion of Hafnium and Zirconium ALD precursor comparison

Here is a very nice review paper from Uwe Schröder and co-workers at NaMLab in Dresden on comparing Hafnium and Zirconium ALD precursors published in the past decades and the selection for mixed HfO2 and ZrO2 ALD high-k and ferroelectric applications.

HfxZr1 − xO2 thin films for semiconductor applications: An Hf- and Zr-ALD precursor comparison editors-pick

Journal of Vacuum Science & Technology A 38, 022402 (2020); https://doi.org/10.1116/1.5134135
Monica Materano, Claudia Richter, Thomas Mikolajick, and Uwe Schroeder

In the last few years, hafnium oxide (HfO2), zirconium oxide (ZrO2), and their intermixed system (HfxZr1 − xO2) have aroused more and more interest due to their outstanding properties in the frame of semiconductor applications. Different mixtures of these two sister materials, i.e., different Hf:Zr ratios in HfxZr1 − xO2 layers, as well as different crystal arrangements come with a wide set of structural and electrical properties, making this system extremely versatile. Starting from an amorphous layer, the different crystalline phases are easier to be targeted through subsequent thermal treatment. A correct understanding of the deposition process could help in obtaining films showing the addressed material properties for the selected application. In this paper, a comparison of Hf- and Zr-atomic layer deposition precursors is conducted, with the goal of depositing an almost amorphous HfxZr1 − xO2 layer. Material composition is tuned experimentally in order to address the properties that are relevant for the semiconductor industry. The observed trends are examined, and guidelines for applications are suggested. 

Growth per cycle for the most common HfO₂ metal precursors as a function of deposition temperature. Except for the Hf[N(CH₃)(C₂H₅)]₄ precursor used in this work, the data have been extracted from other sources. (Reference for HfI4-O2 is wrong, should read ref. 28.)

An ultrathin integrated nanoelectromechanical transducer based on ALD ferroelectric hafnium zirconium oxide

Nanomechanical resonators fabricated with MEMS technology that can operate in the super high frequency (3–30 GHz) or the extremely high frequency (30–300 GHz) regime could be of use in the development of: 

• stable frequency references
• wideband spectral processors
• high-resolution resonant sensors. 

However, such operation requires the dimensions of the mechanical resonators to be reduced to tens of nanometres, and current devices typically rely on transducers, for which miniaturization and chip-scale integration are challenging. 

 

Recently (LINK), researchers at University of Florida were able to fabricate an ultrathin nanoelectromechanical transducer using 10 nm thin ferroelectric hafnium zirconium oxide (Hf_0.5Zr_0.5O₂) films deposited by ALD on a Veeco CNT Fiji.

 

The figure below summarizes the fabrication process flow for implementation of the 70 nm Si nanomechanical resonators actuated using 10nm Hafnium Zirconium Oxide (Hf0.5Zr0.5O2) film.

MEMS manufacturing flow, as published in the Supporting information (free to download LINK) to Ghatge, M., Walters, G., Nishida, T. et al. An ultrathin integrated nanoelectromechanical transducer based on hafnium zirconium oxide. Nat Electron (2019) doi:10.1038/s41928-019-0305-3.

 

Recommended further reading : An ultrathin nanoelectromechanical transducer made of hafnium zirconium oxide, Tech Explore (LINK)

Researchers from University of Groningen, the Netherlands confirm ferroelectricity in nanosized HfO2 crystals

Since the finding of ferroelectricity in HfO2 films of sub 10 nm thickness by Tim Böscke*,  (US8304823B2 NaMLab gGmbH) more then 10 years ago many leading R&D teams and semiconductor companies has confirmed the findings. Now also ferroelectricity in nanosized HfO2 crystalsby has been confirmed by the "Hafnia team” within the Nanostructures of Functional Oxides group, Zernike Institute for Advanced Materials, University of Groningen (UG), the Netherlands (LINK). 

* then at the DRAM Company Qimonda

Figure shows inside view of vacuum chamber in which the process of 'pulsed laser deposition' takes place, used to create the hafnium oxide crystals in this study. On the left the glowing substrate on which the film is growing with atomic control; in the center the blue plasma of ions that is created by shooting a laser on a target with the right chemical composition (target visible on the right side of the figure). | Photo Henk Bonder, University of Groningen

Ferroelectric materials have a spontaneous dipole moment which can point up or down. This means that they can be used to store information, just like magnetic bits on a hard disk. The advantage of ferroelectric bits is that they can be written at a low voltage and power. Magnetic bits require large currents to create a magnetic field for switching, and thus more power. However, according to the scientific community, the aligned dipoles in ferroelectric materials are only stable in fairly large groups; thus, shrinking the crystals results into the loss of dipole moment obstructing ferroelectricity based storage devices.

Nevertheless, eight years ago, the first publication by ex-Qimonda experts and researchers from Fraunhofer and RWTH Aachen (Appl. Phys. Lett. 99, 102903 (2011); https://doi.org/10.1063/1.3634052) announced that hafnium oxide thin films were ferroelectric when thinner than ten nanometres and that thicker films actually lost their ferroelectric properties. This triggered many groups across the globe to dig deeper and confirm the claim of researchers from NamLab. Noheda and her group at University of Groningen was also one of them. Since the ferroelectric hafnium oxide samples used in the study carried out at NaMLab were polycrystalline and showed multiple phases, obscuring any clear fundamental understanding of such an unconventional phenomenon, Noheda and her group decided to study these crystals by growing clean (single-phase) films on a substrate.

Using X-ray scattering and high-resolution electron microscopy techniques, the group observed that very thin films (under ten nanometres) grow in an entirely unexpected and previously unknown polar structure, which is necessary for ferroelectricity. Combining these observations with meticulous transport measurements, they confirmed that the material was indeed ferroelectric. Surprisingly, they noticed that the crystal structure changed when the layers exceeded 10 nm, thus reaching the same conclusion as of the Namlab.

In the substrate that UG researchers used, the atoms were a little bit closer than those in hafnium oxide which strained hafnium oxide crystals a little. Moreover, at a very small size, particles have a very large surface energy, creating pressures of up to 5 GPa in the crystal. This altogether forces a different crystal arrangement and in turn polar phase in the HfO2 film.

One contradicting finding of the UG researchers is that the HfO2 crystals do not need a ‘wake-up’ cycle to become ferroelectric. The thin films investigated at NamLab turned ferroelectric only after going through a number of switching cycles (wake-up cycles) needed to align the dipoles in “uncleaned” samples grown via other techniques. In case of the pulsed laser deposition setup and the substrate used at UG, the alignment is already present in the crystals.

Meanwhile, NaMLab has explored ferroelectric properties in atomic layer deposition (ALD) based thin-films of doped HfO2, and has achieved revolutionary results (LINK). A variety of dopant materials (Si, Al, Ge, Y, Gd, La and Sr) with a crystal radius ranging from 50 to 130 pm has been studied in addition to a mixed Hf1-xZrxO2. The aim is to develop a memory concept with the HfO2 based ferroelectric transistors (FeFET) as building blocks. The FeFET is a long-term contender for an ultra-fast, low-power and non-volatile memory technology. In these devices the information is stored as a polarization state of the gate dielectric and can be read non-destructively as a shift of the threshold voltage. The advantage of a FeFET memory compared to the Flash memory is its faster access times and much lower power consumption at high data rates. In the framework of a project together with GLOBALFOUNDRIES and Fraunhofer IPMS, which was funded by the Free State of Saxony, a one-transistor (1T) FeFET eNVM was successfully implemented at NaMLab in a 28 nm gate-first super low power (28SLP) CMOS technology platform using only two additional structural masks (LINK). The electrical baseline properties remain the same for the FeFET integration, demonstrating the feasibility of FeFET as low-cost eNVM.

Guest Blog by: Abhishekkumar Thakur, Fraunhofer IKTS / TU Dresden
Location: Dresden, Germany

LinkedIn: www.linkedin.com/in/abhishekkumar-thakur-16081991