Simon Min Sze

Overview of emerging nonvolatile memory technologies

Nonvolatile memory technologies in Si-based electronics date back to the 1990s. Ferroelectric field-effect transistor (FeFET) was one of the most promising devices replacing the conventional Flash memory facing physical scaling limitations at those times. A variant of charge storage memory referred to as Flash memory is widely used in consumer electronic products such as cell phones and music players while NAND Flash-based solid-state disks (SSDs) are increasingly displacing hard disk drives as the primary storage device in laptops, desktops, and even data centers. The integration limit of Flash memories is approaching, and many new types of memory to replace conventional Flash memories have been proposed. Emerging memory technologies promise new memories to store more data at less cost than the expensive-to-build silicon chips used by popular consumer gadgets including digital cameras, cell phones and portable music players. They are being investigated and lead to the future as potential alternatives to existing memories in future computing systems. Emerging nonvolatile memory technologies such as magnetic random-access memory (MRAM), spin-transfer torque random-access memory (STT-RAM), ferroelectric random-access memory (FeRAM), phase-change memory (PCM), and resistive random-access memory (RRAM) combine the speed of static random-access memory (SRAM), the density of dynamic random-access memory (DRAM), and the nonvolatility of Flash memory and so become very attractive as another possibility for future memory hierarchies. Many other new classes of emerging memory technologies such as transparent and plastic, three-dimensional (3-D), and quantum dot memory technologies have also gained tremendous popularity in recent years. Subsequently, not an exaggeration to say that computer memory could soon earn the ultimate commercial validation for commercial scale-up and production the cheap plastic knockoff. Therefore, this review is devoted to the rapidly developing new class of memory technologies and scaling of scientific procedures based on an investigation of recent progress in advanced Flash memory devices.

Rapid-Thermal-Processed BaTiO3 Thin Films Deposited by Liquid-Source Misted Chemical Deposition

BaTiO3 thin films deposited on the RuO2(250 nm)/Ru(20 nm)/TiN(200 nm)/Ti(20 nm)/(100)Si substrates by liquid-source misted chemical deposition are reported. The rapid thermal processing (RTP) technique was used for post deposition annealing. It was found that the strain was released and grain size increased for BaTiO3 films treated at high RTP temperature or for long RTP time. The interface between BaTiO3 and the bottom electrode was still sharp for the RTP-treated sample at 950°C. The leakage current density decreases as the RTP temperature increases. It can be decreased to 2.09 nA/cm2 under a supply voltage of 1.5 V. The dielectric constant can be increased up to 250 measured at 100 kHz for the sample treated by RTP at 950°C. The improvements in the BaTiO3 characteristics are due to the fact that RTP can enhance the crystallinity, relax the strain, alleviate the impurities in the films and does not result in significant interdiffusion of the materials.

Effects of O2 plasma treatment on the electric and dielectric characteristics of Ba0.7Sr0.3TiO3 thin films

Abstract The effects of the O2 plasma treatment on the electric and dielectric characteristics of Ba0.7Sr0.3TiO3 (BST) thin films were investigated. As a result of the exposure of the as-deposited or the annealed BST films to the O2 plasma, the leakage current density of the BST films can be improved. Typically, the leakage current density can decrease by three orders of magnitude as compared that of the non-plasma treated sample at an applied voltage of 1.5 V. It is found that the plasma treatment changes the surface morphology. The capacitance of the BST films was reduced by 10%∼30%. The improvement of the leakage current density and the reduction of a dielectric constant for the plasma treated samples could be attributed to the reduction of carbon contaminations of BST thin films. The 10 year life time of the time-dependent dielectric breakdown (TDDB) studies indicates that all the samples have a life time of over 10 years of operation at a voltage bias of 1 V.

Co-sputtered Ru-Ti alloy electrodes for DRAM applications

Abstract Co-sputtered Ru-Ti alloy films were studied for use as a bottom electrode for ferroelectric/paraelectric thin film capacitors. The Ru/Ti ratio in the alloy was found to strongly affect the resistivity, structure formation and thermal stability. The resistivity of the as-deposited films decreases and approaches that of pure Ru metal films as the amount of Ru atoms increases. From X-ray diffraction measurements, it was found that the RuTi phase has formed for the as-deposited sample. The resistivity of alloy thin films is thermally stable as the Ru composition varies from 0.68 to 0.81. It may be due to RuTiO2 formation at the surface and play an important role in preventing further oxidation of the Ru-enriched layer. This oxide also exhibits conductive behavior. On the other hand, the interface between Ru-enriched alloys and Si substrate was still sharp for the sample treated by rapid thermal processing at 600 °C for 1 min. The alloy film with high Ru composition shows excellent thermal stability and barriers against interdiffusion of Si and oxygen.

Growth and electrical characterization of Si delta‐doped GaInP by low pressure metalorganic chemical vapor deposition

The growth and electrical characterization of Si delta‐doped GaInP grown by low‐pressure metalorganic chemical vapor deposition are reported in this article. It was found that the sheet carrier density saturated as a function of doping time or flow rate. Because of the limitations of Hall‐effect measurements, the saturation was explained as the result of electron population in satellite L valley. The mobility enhancement was observed for the delta‐doped structure with an enhancement factor of 2–3. A sharp capacitance–voltage profile with a full width at half‐maximum of 30 A was obtained. Depletion‐mode Si delta‐doped GaInP field‐effect transistors with a gate length of 2 μm and gate width of 50 μm were fabricated and showed good device pinch‐off characteristics. The extrinsic maximum transconductance of 92 mS/mm was obtained and a broad plateau transconductance profile was observed to confirm the electron confinement in the V‐shape potential well of a delta‐doped GaInP layer.

Ion-implanted treatment of (Ba, Sr)TiO3 films for DRAM applications

Abstract The effects of ion implantation on the properties of spin-on sol–gel Ba0.7Sr0.3TiO3 (BST) thin films were studied by implanted Ar+, N+, and F+ doses. The F+-implanted BST samples present leakage current density 10 −6 A / cm 2 at 2.5 V and dielectric constant ∼450. The leakage current of F+-implanted BST samples was reduced about one order of magnitude as compared with that of samples with implanted Ar+, N+ or without implantation. The thickness shrinkage from 135 to 115 nm was observed in F+-implanted BST films (before annealing treatment) and a respective increase in the refractive index from 1.84 to 2.05 was measured. After annealing the implanted samples, the changes of thickness and refractive index depend on the concentration of implanted dose. Based on an infrared transmission study of the samples we suggest that the ion-implanted samples with smaller dose (5×10 14 cm −2 ) have fewer −OH contaminants than the non-implanted or implanted samples with the larger doses (⩾ 1×10 15 cm −2 ). Based on the results presented, we conclude that suitable ion implantation densifies the spin-on sol–gel BST films and reduces the −OH contaminants in the films.

Characterization of NH3 plasma-treated Ba0.7Sr0.3TiO3 thin films

Abstract The effects of plasma surface treatment, using NH 3 gas, of Ba 0.7 Sr 0.3 TiO 3 (BST) films on the leakage and dielectric characteristics of a Pt/BST/Pt capacitor were investigated. As a result of the exposure of BST to the plasma, the leakage current density of the BST capacitor can be improved by three orders of magnitude as compared to that of the non-plasma-treated sample at an applied voltage of 1.5 V. Nevertheless, the surface morphology of BST was also changed by the NH 3 plasma, as explored by atomic force microscopy. From the X-ray photoelectron spectroscopy examination, the existence of the N 1 s peak was observed in the plasma-treated sample. It induces the additional space charge and results in the reduction of the dielectric constant.

Effects of fluorine-implanted treatment on Ba0.7Sr0.3TiO3 films

Abstract The effects of F-ion implantation on the leakage and dielectric properties of the Ba0.7Sr0.3TiO3 (BST) films were investigated. The BST film implanted with 1×1015 cm–2 shows the optimum leakage performance. The leakage current density can be decreased by one order of magnitude as compared to that of the non-implanted sample at an applied voltage of 2 V. On increasing the implanted dose from 5×1014 to 5×1015 cm–2, the dielectric constant first increases and then decreases due to the deteriorated crystallinity. It is found that the suitable F-ion dose can reduce the –OH contaminants and improve the dielectric and leakage properties.