What fuels progress in the rapidly changing semiconductor world? While invention is the driver behind many advancements, reimagining the use of existing technologies for new applications can also overcome barriers to progress. This latter approach enabled SK hynix to make huge strides in the mobile DRAM field.

While the semiconductor industry struggled to continue mobile DRAM scaling¹, SK hynix made a significant breakthrough with the world’s first application of High-K Metal Gate (HKMG) to mobile DRAM. Through this innovative use of the long-established HKMG process, the company was able to develop next-generation LPDDR² products which set new standards in performance.

¹Scaling: The reduction in size of semiconductors to produce better device performance, power efficiency, and cost.
²Low Power Double Data Rate (LPDDR): Low-power DRAM products for mobile devices, including smartphones and tablets, aimed at minimizing power consumption and featuring low voltage operation.

This Rulebreakers’ Revolutions episode focuses on SK hynix’s groundbreaking application of HKMG and the challenges the company overcame to integrate this process to mobile DRAM.

The Mission: Tackle Power Loss Issues to Continue Mobile DRAM Scaling

The growth of on-device AI and other applications is placing ever-increasing performance demands on mobile devices. In turn, mobile DRAM must continue scaling down and provide faster processing speeds to support these applications while maintaining low-power consumption. However, there are issues with the continued miniaturization of mobile DRAM transistors through traditional processes.

A DRAM typically includes cell transistors which store data and peripheral (peri.) transistors responsible for data input and output. To improve DRAM performance, it is necessary to scale down transistors which brings the source³ and drain⁴ closer together and increases the current. However, to reduce power consumption, the operating voltage to the gate⁵ must be decreased. Consequently, the gate insulating film must be thinned to improve transistor performance at a lower voltage.

In standard DRAM products including mobile DRAMs, this insulating film is generally made from silicon oxynitride (SiON) which encounters reliability issues when reduced in thickness. Moreover, the thinning of SiON insulators increases the amount of leakage current⁶, leading to a loss of power. This is a significant issue for battery-powered mobile devices in which low-power consumption is critical to extend the usage time on a single charge.

³Source: The terminal through which the majority charge carriers enter the transistor.
⁴Drain: The terminal through which the majority charge carriers exit from the transistor.
⁵Gate: A component in a transistor that controls the flow of electric current by acting as an on-off switch.
⁶Leakage current: Unwanted flow of electrical current that occurs when the transistor is in the off state.

SiON insulators in conventional transistors are a barrier to DRAM scaling

To tackle this power consumption issue and ultimately ensure the continued scaling of mobile DRAM without compromising performance, SK hynix once again broke the rules of convention and turned to a long-standing technology—HKMG.

The Future Lies in The Past: World-First HKMG Application & Integration Challenges

HKMG was commercialized over a decade ago, first used in logic semiconductors and then applied to high-performance DRAM memory. Although HKMG was an established technology, SK hynix was the first company to see it as a solution to the scaling limitations of mobile DRAM while others continued with traditional processes. This pioneering application of HKMG and optimization of the process revolutionized the mobile DRAM sector, paving the way for ultra-low-power and ultra-high-speed solutions.

The groundbreaking application of HKMG enabled mobile DRAM to continue scaling

So what is HKMG and how does it solve the issues of the traditional SiON process? The HKMG process involves replacing the traditional SiON insulator in transistors with a thin High-K film which prevents leakage currents and improves reliability. Offering high levels of permittivity⁷, High-K film provides equivalent electrical characteristics as a film five times thicker. This thinner film enables continuous transistor scaling, resulting in faster speeds and lower power characteristics compared to SiON-based transistors.

⁷Permittivity: Degree of how many electrons can be stored inside a gate.

The HKMG process tackled the power and performance issues associated with SiON insulators in conventional transistors

As the whole HKMG process had never been applied to mobile DRAM before, SK hynix had to optimize the process and overcome challenges to ensure its smooth application. One of the most significant risks the company recognized was the potential for defects to arise from the application of HKMG to mobile DRAM. In particular, when applying the HKMG process to an LPDDR product for the first time, various stability issues arising from the use of new materials could cause chip defects. To combat this, SK hynix conducted preliminary evaluations through pilot products. Through these various evaluations and tests along with leveraging cross-company expertise, SK hynix was able to maximize transistor performance and ultimately secure the integrated process solution for mobile DRAM.

Unlocking New LPDDR Solutions

The first-ever mobile DRAM products made with the HKMG process offered huge leaps in power and speed

The successful integration of the HKMG process with mobile DRAM paved the way for SK hynix to develop new ultra-low-power and rapid LPDDR solutions. In November 2022, the company released the world’s first ever mobile DRAM with the integrated HKMG process, Low Power Double Data Rate 5X (LPDDR5X). The product offered ultra-low operating power of 1.01–1.12V and an operating speed of 8.5 Gbps. LPDDR5X is 33% faster and uses 21% less power compared to the previous generation, ensuring it meets both sustainability goals to lower carbon emissions and technological targets.

Just two months later, SK hynix once again set new standards in mobile DRAM with the introduction of Low Power Double Data Rate Turbo (LPDDR5T). While LPDDR5T operates at the same low voltage as LPDDR5X and provides a 21% reduction in power consumption from LPDDR5, it also offers significant leaps in speed from its predecessor. At the time of its release, LPDDR5T was the world’s fastest mobile DRAM, boasting an impressive operating speed of 9.6 Gbps—13% faster than LPDDR5X and 50% quicker than LPDDR5. Such speeds were only thought of as possible with the next-generation LPDDR6, but the company was able to reach new heights ahead of schedule thanks largely to the application of HKMG.

Rulebreaker Interview: Jongchan Choi, Product Solution Process Integration

To learn more about the “rulebreaking” approach which led to the application of HKMG to mobile DRAM, the SK hynix newsroom interviewed Team Leader Jongchan Choi of Product Solution Process Integration. Choi, who helped develop the process solution when HKMG was first applied to LPDDR products, discusses the future direction of HKMG and its potential future applications beyond mobile DRAM.

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The post [Rulebreakers’ Revolutions] How SK hynix Broke Barriers in Mobile DRAM Scaling With World-First HKMG Application first appeared on SK hynix Newsroom.

From breaking barriers for performance with HBM3 to developing the world’s fastest mobile DRAM, LPDDR5T, SK hynix’s product portfolio is full of industry-leading solutions which have pushed technological limits. But how exactly does the company realize this rapid evolution in its solutions? What innovations and processes are applied to these products to take them to the next level?

To shed light on these technologies, SK hynix Newsroom is launching its seven-part Tech Pathfinder series. The articles in the series will introduce some of the company’s most advanced products globally renowned for their unprecedented qualities including industry-leading processing speed, data storage, and computational capabilities. Through the series, readers will gain a better grasp of the concepts behind these innovative products and gradually become more familiar with the advancement of semiconductors and technology in general.

SK hynix’s Secret Behind Its DRAM Development

In November 2022, SK hynix released a mobile DRAM with the world’s lowest operating power of 1.01-1.12V and an operating speed of 8.5 Gbps—Low Power Double Data Rate 5X (LPDDR5X). The company then made another historic step in January 2023 with the development of its Low Power Double Data Rate 5 Turbo (LPDDR5T), the world’s fastest mobile DRAM which offers an operating speed of 9.6 Gbps.

▲ Figure 1. SK hynix’s LPDDR5 Lineup Made With the HKMG Process

Smartphone mobile DRAMs need to be small, low-power devices which provide fast processing speeds to perform more functions. However, as the industry reaches the limits of scaling¹, such mobile DRAM technology only becomes more complex. So, what is the secret in SK hynix’s technology that has allowed the company to remain a powerhouse in mobile DRAM development? The answer lies in the world’s first application of the High-K Metal Gate (HKMG) process to mobile DRAM. This article will summarize the principle of the HKMG process and how this technology was applied to the LPDDR5X and LPDDR5T.

¹Scaling: The reduction in size of semiconductors to produce better device performance, power efficiency, and cost.

HKMG Process: Key to the World’s Fastest Mobile DRAM With Lowest-Power Consumption

▲ Figure 2. SK hynix Applies HKMG Process to Develop the World’s Fastest Mobile DRAM

Although HKMG was commercialized over a decade ago, various challenges were encountered during the development of this groundbreaking technology. There were four major obstacles: the extreme complexity of the technology, the high-processing cost compared to conventional materials, unpredictable risks, and the difficulty in controlling electron leakage. More importantly, the whole HKMG process had never been applied to mobile DRAM before. Despite facing these issues, SK hynix took on the challenge of changing the paradigm of mobile DRAMs.

More specifically, applying the HKMG process to mobile DRAM peripheral (peri) transistors posed a major challenge. DRAMs typically consist of cell transistors which store data and peri transistors which conduct data input and output. It is therefore necessary to minimize the impact of the HKMG process on the cell as the connection between the cell and peri transistor can encounter problems when applying the HKMG process to the periphery.

Accordingly, the area of the peripheral circuit that powers the cell is also reduced as the cell scale is minimized. This leads to a shrinking of the transistors that supply the charge, which, consequently, reduces the thickness of the gate insulator. These insulators for conventional mobile DRAMs are generally made from silicon oxide (SiON), which suffers from speed limitations when it is thinned. SiON also faces an efficiency problem as, when the thickness of the insulator decreases, the amount of leakage current increases and this leads to a loss in power.

SK hynix’s solution to these issues was to apply High-K material to the insulation film as the material has a permittivity² that is about five times higher than conventional SiON insulation film. To put this into context, when the same voltage is applied, the High-K insulation film can keep five times more charge than a conventional SiON material with the same area and thickness. This means that the thickness and leakage current can be reduced by making the insulation film with High-K material.

²Permittivity: Degree of how many electrons can be stored inside a gate.

However, the combined use of polysilicon (poly-Si)—applied in existing gates—and High-K materials increased the gate’s resistance, so a higher voltage is required and electrons slow down. To combat this, the poly-Si gate was replaced with a metal gate. With the combination of a gate oxide that possesses a high permittivity and a metal electrode, SK hynix successfully created an integrated HKMG solution.

▲ Figure 3. Description of HKMG Technology

Pioneering the Application of the HKMG Process

In preparation for the development stage, SK hynix first set up a taskforce comprised of device and process experts in the development, research, and manufacturing fields. The taskforce, the first of its kind for a derivative product³, consisted of members of the and PE (Product Engineering) team. Having begun working together from the initial stages of the process development, the taskforce resolved issues such as reliability and quality risks. Their main goal was to develop an integrated solution incorporating HKMG technology to the existing process while minimizing costs by maintaining parts of the existing process as much as possible.

³Derivative product: A product that is derived from a core product. Core products, a kind of prototype in which existing technology and elements are applied, allow manufacturers to establish a leadership position in the related technology as they can be quickly developed. The resultant derivative products feature various capacity and performance modifications to meet market needs.

It was also necessary to develop a method for utilizing the characteristics of the HKMG process to both increase speed and reduce power usage. However, due to the limitations in the chip’s size, lowering the electrical capacity to reduce power was not possible. Consequently, it became necessary to create a design that would lower the voltage. To this end, innovative design ideas were produced which eventually led to low-power solutions. These solutions included using a power architecture that would lower the design’s internal power and lowering the gate level in sleep mode to significantly reduce power consumption.

SK hynix Rewrites the Rules With LPDDR5X and LPDDR5T

▲ Figure 4. SK hynix’s World-First Application of HKMG Process to Mobile DRAM Enables Ultra-High Speed & Ultimate Power Efficiency

While effectively controlling leakage current, LPDDR5X offers a 33% increase in speed (8.5 Gbps) and a 21% power usage reduction compared to the previous generation. This increase in energy efficiency ensured the product reached its environmental goal of carbon reduction as well as meeting target technological specifications. Skip forward two months and LPDDR5T was developed. Operating in the same ultra-low voltage range as LPDDR5X, it is 13% faster at 9.6 Gbps to make it the fastest mobile DRAM available today.

SK hynix’s mobile DRAM which applies the HKMG process has been praised for its world-class performance. The company is also promoting the establishment of a new specification for mobile DRAM at the Joint Electron Device Engineering Council (JEDEC). SK hynix’s next step is to actively leverage the experience gained from the successful development of the HKMG process to bring even greater innovation to the next generation of technologies and products. In other words, LPDDR5X and LPDDR5T are just the beginning.

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The post [Tech Pathfinder] HKMG Opens the Door to Leading Mobile DRAM LPDDR5X & LPDDR5T first appeared on SK hynix Newsroom.