A Ferroelectric tunnel junction (FTJ) is a form of tunnel junction including a ferroelectric dielectric material sandwiched between two electrically conducting materials. Electrons do not directly pass through the junction, and instead they pass the barrier via quantum tunnelling. The structure is similar to a ferroelectric capacitor, but the ferroelectric layer is fabricated thin enough to enable significant tunneling current. The magnitude of the tunneling current is switched by the ferroelectric polarization and is governed by the tunneling electroresistance (TER).

There exists two conditions that must be met in order to manufacture a reliable FTJ: the FE-layer must be at maximum 3 nm in order to allow the electron tunneling (see section tunneling), and the interfaces on both sides need to be energetically asymmetrical in order to obtain two separate potential barrier heights.

Ferroelectric tunnel junctions are being developed as a memristive component for the semiconductor industry. As of early 2024, FTJ based technologies are not commercially available. To enable sufficient tunneling probability, the ferroelectric layer must be thin enough (in the nanometer scale), rendering many conventional ferroelectric materials redundant. Ferroelectricity as a phenomenon was long thought to disappear in thicknesses required for tunneling, which hindered research around the topic until the 2000s. Since, significant ferroelectricity has been shown in thin films, and FTJs have been successfully shown to follow the proposed working principle.

While most ferroelectric materials require high fabrication temperatures, polycrystalline thin film hafnium oxide has been shown to be ferroelectric even with back-end complementary metal oxide semiconductor (CMOS) compatible fabrication temperatures, rendering FTJs especially interesting for the semiconductor industry.

The hafnium oxide is deposited using atomic layer deposition (ALD) to enable precise growth to form thin enough layers. FTJs have gained significant interest due to the memristive properties as well as CMOS compatible operating voltages and fabrication methods. In addition to ferroelectric tunnel junctions, there are other ferroelectric devices, including ferroelectric capacitors (FeCAP), ferroelectric field-effect transistors (FeFET), ferroelectric random-access memory (FeRAM) and multiferroic tunnel junctions (MFTJ), which are ferroelectric tunnel junction with ferromagnetic materials as the two electrodes.

Ferroelectric tunnel junctions are devices where the current through the device can be controlled by the voltage driven across the device. These memristive components use ferroelectric behavior to change the tunneling probability through the device.

In a simple explanation of ferroelectricity, the electric dipole moments of the crystalline unit cells point first in random directions. As a voltage is driven across the material, these dipole moments rotate to align with the electric field induced by the voltage difference. Once the voltage is lowered back to zero, the dipole moments remain aligned with the previous field. The sum of individual dipole moments form the polarization of the material. In non-ferroelectric materials the polarization relaxes back to zero once the voltage is brought down; in ferroelectric materials the polarization remains. When a voltage of the opposite sign is driven through the same piece of ferroelectric material, the polarization switches to point in the opposite direction. Again, the polarization remains even after the field is reduced to zero. This results in a hysteresis effect seen in the polarization-electric field (PE) curve.

Switching the ferroelectric polarization of the material affects the height of the potential barrier in the device. The potential barrier influences the tunneling probability and thus the current measured, which can be utilized as voltage-controlled memory.