Robust switching characteristics of CdSe/ZnS quantum dot non-volatile memory devices

Abstract

In this paper we report Al/CdSe-ZnS core-shell quantum dot/AlOx/CdSe-ZnS core-shell quantum dot/ITO based non-volatile resistive memory devices with an ON/OFF ratio of ~1000. The facile solution processed device exhibited excellent endurance characteristics for 200,000 switching cycles. Retention tests showed good stability for over 20,000 s and the devices are reproducible. A memory operating mechanism is proposed based on charge trapping-detrapping in core-shell quantum dots with AlOx acting as a barrier leading to Coulomb blockade. I-V characteristics of a three terminal device fabricated with the additional terminal wired-out from the middle AlOx layer supports the proposed charge trapping mechanism.

An Organic/Inorganic Nanomaterial and Nanocrystal Quantum Dots-Based Multi-Level Resistive Memory Device

“…As the QDs are embedded in the partially oxidized aluminum layer, NCs are formed. Since the formation of the NCs allows the QDs formed at the bottom and the QDs formed at the top to be isolated from each other, it can be applied as a bi-stable memory [22,45,47]. In the AFM result of forming only QDs as a thin film in…”

“…As the QDs are embedded in the partially oxidized aluminum layer, NCs are formed. Since the formation of the NCs allows the QDs formed at the bottom and the QDs formed at the top to be isolated from each other, it can be applied as a bi-stable memory [22,45,47]. In the AFM result of forming only QDs as a thin film in (Figure 6a), the root-mean-squared (RMS) roughness was 0.28, but the RMS roughness of the QDs thin film deposited on partially oxidized aluminum (Figure 6b) was 0.92, showing a significant increase.…”

“…QDs are semiconductor materials with a size of 2 to 10 nm and consist of a core that determines the band gap of the QDs, a shell that protects the unstable core, and a ligand that determines the reactivity of the QDs [20,21]. In particular, the QDs includes a quantum well with a core/shell structure, and can thus be used as a substitute for an oxide-based resistive layer [22][23][24][25][26][27][28]. Depending on whether charges are trapped in the quantum well, the conductivity (resistance) of the charge storage layer (CSL) composed of QDs changes.…”

“…Depending on whether charges are trapped in the quantum well, the conductivity (resistance) of the charge storage layer (CSL) composed of QDs changes. Before the trap site is filled, a small current flows through the device as external charges are trapped in the QDs (high resistance state, HRS); however, after the trap site is filled, it is no longer trapped and a large current flows through the device (low resistance state, LRS) [22,29,30]. The charge trapped in the quantum well is due to a high energy barrier, so de-trapping does not occur until [3] an external voltage is applied.…”

CdSe quantum dot/AlOx based non-volatile resistive memory

“…While the physical limit of the write time for quantum dots is in the picoseconds range. Quantum dots embedded in a partially oxidized thin aluminum/titanium layer exhibited bipolar bistable non-volatile memory characteristics with excellent ON/OFF ratio and fast switching times [19][20][21]. In this paper, we present a bipolar non-volatile resistive memory device, exclusively based on spin casted quantum dot/metal/quantum dot structure with ON/OFF ratio [10,000 with CdSe quantum dot size *5.2 nm.…”