Researchers discover a new pathway to building energy-efficient computing chips - Berkeley Engineering

The demand for more energy-efficient computing chips is growing as electronic devices become more popular. Researchers have now found a way to change the electronic properties of a common semiconductor material. This discovery could lead to faster, lower-power data storage and processing.

Unlocking New Properties in Titanium Dioxide

A team led by UC Berkeley found that titanium dioxide (TiO₂) can become a ferroelectric material when made extremely thin. They reduced its thickness to less than three nanometers, which is about the size of a single strand of human DNA. This finding could pave the way for tiny, energy-efficient electronic devices.

Ferroelectric materials can switch their electric polarization. This property has been important in the semiconductor industry for a long time. Many experts believe these materials are key to creating the next generation of energy-efficient nanoelectronics. This includes non-volatile memory, logic devices, and new computing technologies.

However, it has been hard to make ferroelectric materials work well when they are ultrathin, which is crucial for small semiconductors. Another challenge has been finding a ferroelectric material that works with existing silicon-based technologies.

To tackle these issues, researchers from UC Berkeley, Lawrence Berkeley National Laboratory, and SLAC National Accelerator Laboratory studied TiO₂. This material is often used in computer chips as a dielectric, meaning it stores electrical charge but doesn't show electric polarization. The researchers discovered that simply making TiO₂ ultrathin changed its electronic properties.

Sayeef Salahuddin, a professor of electrical engineering and computer sciences, noted that engineering materials at an atomic scale can reveal unexpected physical phenomena.

Salahuddin, the study's main investigator, said they were surprised when TiO₂ films thinner than three nanometers became ferroelectric. This means the material showed spontaneous electric polarization that could be switched with an electric field. He added that this new ferroelectric behavior remained stable even in films as thin as one nanometer, which is about two unit-cells thick.

Implications for Future Computing

This study suggests that reducing a material's thickness could be a new way to control ferroelectricity and phase transitions. Salahuddin also believes that other common dielectric materials, like binary oxides, might develop new electronic behaviors at atomic-scale dimensions.

Koushik Das, a graduate researcher and the study's lead author, explained that making TiO₂ film thinner changes its crystal structure. This creates a "built-in electric polarization" that can be reversed with an electric field.

The study also showed that these ultrathin TiO₂ films kept their ferroelectric properties when placed on different surfaces. Das noted that this ferroelectricity is stable on both crystalline (silicon) and amorphous carbon film substrates. This means it could be integrated with silicon-based technologies and beyond.

Das also highlighted that TiO₂ is compatible with current semiconductor manufacturing processes. He said that ultrathin TiO₂ films can be grown at low temperatures (less than 400°C) using atomic layer deposition (ALD). This technique is already used in advanced chip fabrication. He added that they can produce thin films with uniform thickness and polarization properties, which could enable new functions for 3D integrated electronics.

Salahuddin believes this work offers a broader scientific insight beyond its immediate technological uses. He stated that simply reducing a material's thickness can fundamentally change its properties and unlock new functionalities with many exciting applications.

The study was published in Science.

Deep Dive & References: Ultrathin titanium dioxide film exhibits surprising properties that could advance semiconductor technology - Science, 2024