Ferroelectric Nitride Heterostructures on CMOS Compatible Molybdenum for Synaptic Memristors

Abstract

Achieving ferroelectricity in III-nitride (III-N) semiconductors by alloying with rare-earth elements, e.g., scandium, has presented a pivotal step toward next-generation electronic, acoustic, photonic, and quantum devices and systems. To date, however, the conventional growth of single-crystalline nitride semiconductors often requires the use of sapphire, Si, or SiC substrate, which has prevented their integration with the workhorse complementary metal oxide semiconductor (CMOS) technology. Herein, we demonstrate single-crystalline ferroelectric nitride semiconductors grown on CMOS compatible metal−molybdenum. Significantly, we find that a unique epitaxial relationship between wurtzite and body-centered cubic crystal structure can be well maintained, enabling the realization of single-crystalline wurtzite ferroelectric nitride semiconductors on polycrystalline molybdenum that was not previously possible. Robust and wake-up-free ferroelectricity has been measured, for the first time, in the epitaxially grown ScAlN directly on metal. We further propose and demonstrate a ferroelectric GaN/ScAlN heterostructure for synaptic memristor, which shows the capability of emulating the spike-time-dependent plasticity in a biological synapse. This work provides a viable path for the integration of III-N architectures with the mature CMOS technology and sheds light on the promising applications of ferroelectric nitride memristors in neuromorphic computing.

Dawn of nitride ferroelectric semiconductors: from materials to devices

“…Most recently, by growing GaN/ScAlN/Mo heterostructures, we were able to demonstrate a semiconductor/ferroelectric/Metal memristor with the opposite ON/OFF operation compared with above Metal/ScAlN/GaN configuration, further confirming the ferroelectric tuning of the interface barrier height [217]. This ferroelectric heterostructure also shows capability of emulating the spike-time-dependent plasticity in a biological synapse.…”

“…[5, 14, 16, 20, 43, 60-62, 64, 123, 145]. b [10,15,19,24,32,45,47,48,69,91,106,125,217,225]. c [51][52][53].…”

Synthesis and Characteristics of Transferrable Single‐Crystalline AlN Nanomembranes

“…It is well known that in the ABF–STEM image, the darkest spots correspond to the heaviest atoms. [ 65,66 ] Therefore, we are able to configure the atomic stacking sequence of Al and N atoms, which is embedded in the ABF–STEM image (Figure 2c). Comparing with the atomic structure of wurtzite AlN, we confirmed that the lattice‐polarity of the transferred AlN membrane is N‐polar.…”

Effect and Regulation Mechanism of Post-deposition Annealing on the Ferroelectric Properties of AlScN Thin Films

“…The thickness of the oxide layer at the interface is determined by the depth profile of the elements and is approximately 21.4 nm (see Figure S7, Supporting Information). These results suggest that annealing temperatures higher than 400 °C increase the risk of oxidation because of the significant oxygen affinity of Sc and Al. − According to the previous report, the intensity of polarity for AlN films will be reduced during the formation of Al x O y N z due to the fact that Al x O y N z has a multiphase structure, which reduces the relative displacement of metal atoms and nitrogen atoms from the common plane . Furthermore, depolarization fields in ferroelectric capacitors also have a drastic effect on the remnant polarization and can be described by the following equation: , E DP = P true[ ε true( C IS C normalF + 1 true) true] − 1 where P is the polarization induced by an applied voltage, ε is the dielectric constant of the ferroelectric film, C F is a ferroelectric capacitance, and C IS is the semiconductor capacitance (dead layer) in series with the C F .…”