Silicon Microelectronic Technology Research Articles

Memristor switching and integration in ensembles of silicon nanocrystallites

We suggest a memristor device that is based on ensembles of Si nanocrystallites that are embedded in an SO2 matrix, for which we show that its operation is well accounted for by the theory of space charge limited currents. This operation consists of a memristive film that exhibits electronic charge integration properties as well as a potential to provide a quantum confinement controlled spiking behavior. As such, the present system is probably the closest available two-terminal electronic film analog that may imitate the neuron’s function. This system can be considered then, not only as “purely electronic” and “bio-realistic” but also as having the great advantage of being compatible with the silicon microelectronic technology. Corresponding devices have the potential to become practical by their downscaling, on the one hand, and by providing a controllable spiking mechanism on the same device, on the other hand.

Memristor with a ferroelectric HfO2 layer: in which case it is a ferroelectric tunnel junction

New interest in the implementation of ferroelectric tunnel junctions has emerged following the discovery of ferroelectric properties in HfO2 films, which are fully compatible with silicon microelectronics technology. The coercive electric field to switch polarization direction in ferroelectric HfO2 is relatively high compared to classical perovskite materials, and thus it can cause the migration of non-ferroelectric charges in HfO2, namely charged oxygen vacancies. The charge redistribution would cause the change of the tunnel barrier shape and following change of the electroresistance effect. In the case of ambiguous ferroelectric properties of HfO2 ultrathin films, this oxygen-driven resistive switching effect can mimic the tunnel electroresistance effect. Here, we demonstrate two separate resistive switching regimes, depending on the applied voltage, in the same memristor device employing a ferroelectric Hf0.5Zr0.5O2 (4.5 nm) layer. The first regime originates from the polarization reversal, whereas the second one is attributed to the accumulation/depletion of the oxygen vacancies at the electrode interface. The modulation of the tunnel barrier causes the enhancement of ROFF/RON ratio in ∼20 times compared to the tunnel electroresistance effect. The developed device was used to formulate the criteria for unambiguous discrimination between the ferroelectric-and non-ferroelectric resistive switching effects in HfO2-based ferroelectric tunnel junctions.

Morphology of Oxygen Precipitates in RTA Pre-Treated Czochralski Silicon Wafers Investigated by FTIR Spectroscopy and STEM

Rapid thermal annealing (RTA) is a commonly used technique to control precipitation of oxygen in Czochralski silicon wafers (1,2). RTA pre-treatment leads to the formation of intrinsic point defects, mainly vacancies, which are responsible for the enhanced precipitation of oxygen. Oxygen precipitates are widely known as getter sites for metal impurities in the silicon microelectronic technology (3). The getter efficiency of oxygen precipitates depends on their density and morphology (4,5). The density of the precipitates can be controlled by the temperature of RTA and it can be easily determined by preferential etching. The morphology of oxygen precipitates depends on the type and the concentration of dopants, the thermal history, and the annealing temperature and time (6-8). Recently, it was shown that the supersaturation of vacancies impacts the morphology of oxygen precipitates (9). Since RTA pre-treatments introduce vacancy supersaturation in silicon wafers its usage before nucleation annealing could modify the morphology of precipitates compared to wafers without RTA. The morphology of oxygen precipitates can be determined by transmission electron microscopy, however the preparation of samples is demanding. An alternative is the Fourier transform infrared (FTIR) spectroscopy at liquid helium temperature, which also allows distinguishing different types of oxygen precipitates. The oxygen precipitates give rise to absorption bands in the range between 1000 and 1300 cm-1. There are two characteristic broad bands at 1095 cm-1 and at 1225 cm-1 which belong to spherical and plate-like precipitates, respectively (10-12). The sharp bands (1136 cm-1 and satellites and 1205 cm-1) are attributed to interstitial oxygen.In this work, we investigate the morphology of oxygen precipitates by FTIR spectroscopy at liquid helium temperature and by scanning transmission electron microscopy (STEM) in silicon samples pre-treated by RTA at 1250°C for 30s in O2 containing Ar atmosphere subsequently annealed in the temperature range between 800°C and 1000°C in N2. The results show that the morphology of the oxygen precipitates in RTA pre-treated samples depends on the nucleation temperature. Fig. 1 presents absorption spectra of silicon samples pre-treated by RTA at 1250°C and annealed at 800°C (a), 900°C (b) and 1000°C (c) for 64h. As can be seen from the deconvolution of the spectra, the number and position of the bands is different for each annealing temperature. Based on the effective medium theory (EMT) (13) and STEM investigations the absorption bands can be matched to relevant morphologies.

Complementary Logic Gate Arrays Based on Carbon Nanotube Network Transistors

An efficient technique of fabricating high performance n- and p- type single-walled carbon nanotube (SWNT) network field-effect transistors (NET-FETs) is successfully demonstrated. Complementary inverters, NOR, NAND, OR, AND logic gates have been achieved from integrating these p- and n-type SWNT-NET-FETs. The processing technique described here is fully compatible with conventional silicon microelectronic technologies and it is readily suitable for scalable integration.

Fabrication and Characterization of a Back-Illuminated Resonant Cavity Enhanced Silicon Photo-Detector Working at 1.55 μm

In this article, the realization and characterization of a new kind of resonant cavity enhanced photo-detector, fully compatible with silicon microelectronic technologies and working at 1.55 μm, are reported. The detector is a resonant cavity enhanced structure incorporating a Schottky diode, and its working principle is based on the internal photo-emission effect. A comparison between a Schottky diode (Al/Si or Cu/Si) and the Schottky diode fed on a high-reflectivity Bragg mirror is carried out. Considering Al as Schottky metal, no difference in responsivity is obtained; considering Cu as Schottky metal, a three-fold responsivity improvement is experimentally demonstrated.

Band structure of Si-based superlattices Si1-xSnx/Si

The prospects of Si-based optical emitting materials are optimistic because the materials are compatible with silicon microelectronics technology. Therefore, many experimental and theoretical studies are directed to the design of direct band-gap Si-based materials. Based on the core state effect, the electronegativity differences effect of component atoms and the symmetry effect, Si-based superlattices Si1－xSnx/Si were designed. We found that Si0.875Sn0.125/Si is a direct band-gap material. In the density functional theory frame, the results of plane pesupotential method show that Si0.875Sn0.125/Si is a direct band-gap superlattice with minimum band-gap at Γ point. We predict that the band gap of the material is 0.96 eV with the help of GW approximation method.

Silicon photonics in China

Silicon photonics, particularly its compatibility with existing silicon microelectronic technology, has been increasingly studied in recent years. China sees the potential impact on the sustainability of its economic development and is increasing the investment in this new research area. But, the lack of research and manufacture accumulation in silicon microelectronic technology will weigh down the pace of silicon photonics research in China in the years to come.

Silicon based nanogap device for studying electrical transport phenomena inmolecule–nanoparticle hybrids

We report the fabrication and characterization of vertical nanogap electrode devicesusing silicon-on-insulator substrates. Using only standard silicon microelectronicprocess technology, nanogaps down to 26 nm electrode separation were prepared.Transmission electron microscopy cross-sectional analysis revealed the well definedmaterial architecture of the nanogap, comprising two electrodes of dissimilargeometrical shape. This asymmetry is directly reflected in transport measurements onmolecule–nanoparticle hybrid systems formed by self-assembling a monolayer ofmercaptohexanol on the electrode surface and the subsequent dielectrophoretictrapping of 30 nm diameter Au nanoparticles. The observed Coulomb staircaseI–V characteristicmeasured at T = 4.2 K is in excellent agreement with theoretical modelling, whereby junction capacitances of the order of a few10−18 farad and asymmetricresistances of 30 and 300 MΩ, respectively, are also supported well by our independent estimates for the formed doublebarrier tunnelling system. We propose our nanoelectrode system for integrating novelfunctional electronic devices such as molecular junctions or nanoparticle hybrids intoexisting silicon microelectronic process technology.

Si-based emissive microdisplays

Standard silicon microelectronics technology is very attractive for use in microdisplays, because it is the shortest way to highest pixel densities and integration of matrix with column and row drivers into a common chip. Use of nanostructured silicon light-emitting diodes (Si LEDs) may completely solve the problem of low compatibility of display elements and silicon chip. At present time the most suitable kinds of Si LEDs are porous silicon avalanche LEDs. They have such advantages as long operation lifetime, continuous spectrum, low operation voltages and extremely sharp voltage–current characteristic, nanosecond response time and high operation current density. This paper considers the background, approaches and achievements in design of the silicon-based LEDs and high-resolution matrix displays.

Metal-oxide-semiconductor-compatible ultra-long-range surface plasmon modes

Long-range surface plasmons traveling on thin metal films have demonstrated promising potential in subwavelength waveguide applications. In work toward device applications that can leverage existing silicon microelectronics technology, it is of interest to explore the propagation of surface plasmons in a metal-oxide-semiconductor geometry. In such a structure, there is a high refractive index contrast between the semiconductor (n≈3.5 for silicon) and the insulating oxide (typically n≈1.5−2.5). However, the introduction of dielectrics with disparate refractive indices is known to strongly affect the guiding properties of surface plasmons. In this paper, we analyze the implications of high index contrast in 1D layered surface plasmon structures. We show that it is possible to introduce a thin dielectric layer with a low refractive index positioned next to the metal without adversely affecting the guiding quality. In fact, such a configuration can dramatically increase the propagation length of the conventional long-range mode. While this study is directed at silicon-compatible waveguides working at telecommunications wavelengths, this configuration has general implications for surface plasmon structure design using other materials and operating at alternative wavelengths.

Field-effect electroluminescence in silicon nanocrystals

There is currently worldwide interest in developing silicon-based active optical components in order to leverage the infrastructure of silicon microelectronics technology for the fabrication of optoelectronic devices. Light emission in bulk silicon-based devices is constrained in wavelength to infrared emission, and in efficiency by the indirect bandgap of silicon. One promising strategy for overcoming these challenges is to make use of quantum-confined excitonic emission in silicon nanocrystals. A critical challenge for silicon nanocrystal devices based on nanocrystals embedded in silicon dioxide has been the development of a method for efficient electrical carrier injection. We report here a scheme for electrically pumping dense silicon nanocrystal arrays by a field-effect electroluminescence mechanism. In this excitation process, electrons and holes are both injected from the same semiconductor channel across a tunnelling barrier in a sequential programming process, in contrast to simultaneous carrier injection in conventional pn-junction light-emitting-diode structures. Light emission is strongly correlated with the injection of a second carrier into a nanocrystal that has been previously programmed with a charge of the opposite sign.

Fundamentals of Cu/Barrier-Layer Adhesion in Microelectronic Processing

AbstractCopper is most widely used interconnect material in present silicon microelectronic technologies. As such, multiple interfaces formed by a thin Cu layer and other materials must be engineered to achieve the desired chemical, mechanical, and electrical properties. Adhesion between Cu and the barrier layer, as well as between Cu and the dielectric, is of particular interest, due to its role in controlling interfacial stability and Cu electromigration behavior [1]. This work focuses on understanding how the interface chemistry affects adhesion. Firstprinciples density functional theory (DFT) calculations were used to determine chemical adhesion energies of interfaces formed by Cu and various metals considered as a diffusion barrier, including Ta, TiN, and W. Calculations predicted increasing adhesion strength in the order of TiN < Si-doped TiN < TaN < Ta, consistent with wetting experiments done using 100Å thick Cu layer samples. The effects of doping at the interface using light elements (C, N, O) were also determined. Calculations were also done for interfaces of Cu with two different classes of amorphous dielectric materials, i.e. silicon nitride and silicon carbide, for which detailed material characterizations are often difficult and time consuming. Calculations predicted Cu/Si-nitride and Cu/Si-carbide adhesion strengths consistent with 4-pt-bend experiments, including the improvement in adhesion energies when silicon was used to dope the interface. In addition, weaker interfaces provide low-resistance diffusion paths for Cu atoms during electromigration. The first-principles based modeling, validated by select adhesion measurements, provides a predictive approach to effectively determine adhesion strengths and predict electromigration reliability in interconnects.

An integrated optical interferometric nanodevice based on silicon technology forbiosensor applications

Integrated optical sensors have become important in recent years since they arethe only technology which allows the direct detection of biomolecularinteractions. Moreover, silicon microelectronics technology allows massproduction as well as the fabrication of nano-/macrosystems on the sameplatform by hybrid integration of sources, sensors, photodetectors andcomplementary metal-oxide semiconductor electronics.For the fabrication of anoptical sensor nanodevice with an integrated Mach–Zehnder interferometric(MZI) configuration, the optical waveguides must have two main features:monomode behaviour and a high surface sensitivity. In this paper wepresent the development of a MZI sensor based on total internal reflectionwaveguides with nanometre dimensions. The aim is to use these sensors inenvironmental control to detect water pollutants by immunoassay techniques.

Integrated Mach–Zehnder interferometer based on ARROW structures for biosensor applications

The theoretical design, fabrication and characterisation of an evanescent field integrated optical (IO) sensor based on a rib anti-resonant reflecting optical waveguide (ARROW) structure are presented. The optical waveguides are designed to verify two conditions: mono-mode behaviour and high surface sensitivity. The sensor system is fabricated with ‘silicon microelectronics technology’ and it has been tested as a refractometer with glucose solutions of different refractive indices. The feasibility of applying the sensor for immunosensing is shown with antibody/antigen binding experiments.

Silicon microelectronics technology

Two inventions — the bipolar transistor and the integrated circuit — have fundamentally revolutionized the technology of mankind. Within a period of fifty years, the microelectronics industry has increased the number of transistors fabricated on a single piece of semiconductor crystal by a factor of about 100 million, that is, 1.0e10+8, a productivity phenomenon unparalleled in the history of technology and mankind. This paper begins with a historical review of that revolution — from the first integrated circuit to modern very large scale integration (VLSI) technology — and then reviews the development of present-day microelectronics manufacturing technology, based on the concept of the “planar process.” The topics covered include silicon crystal technology, crystal dopant techniques, silicon oxidation development, lithography, materials deposition processes, pattern transfer mechanisms, metal interconnect technology, and material passivation technology. The paper concludes with a review of the major technical and economic issues that face the microelectronics industry today and discusses the future technical and economic paths that the industry may take.

Beyond the conventional transistor

This paper focuses on approaches to continuing CMOS scaling by introducing new device structures and new materials. Starting from an analysis of the sources of improvements in device performance, we present technology options for achieving these performance enhancements. These options include high-dielectric-constant (high-k) gate dielectric, metal gate electrode, double-gate FET, and strained-silicon FET. Nanotechnology is examined in the context of continuing the progress in electronic systems enabled by silicon microelectronics technology. The carbon nanotube field-effect transistor is examined as an example of the evaluation process required to identify suitable nanotechnologies for such purposes.

Radiative recombination processes of thermal donors in silicon

AbstractThere is a recent, renewed attention on the possible development of optical emitters compatible with silicon microelectronic technology and it has been recently shown that light emitting diodes could be manufactured on dislocated silicon, where dislocations were generated by plastic deformation or ion implantation. Among other potential sources of room temperature light emission, compatible with standard silicon-based ULSI technology, we have studied old thermal donors (OTD), as the origin of their luminescence is still matter of controversy and demands further investigation.In this work we discuss the results of a spectroscopical study of OTD using photoluminescence (PL) and Deep Level Transient Spectroscopy (DLTS) on standard Czochralsky (Cz) silicon samples and on carbon-doped samples.We were able to show that their main optical activity, which consists of a narrow band at 0.767 eV ( P line), is correlated to a transition from a shallow donor level of OTD to a deep level at EV+0.37 eV which is tentatively associated to C-O complexes. As we have shown that the P line emission persists at room temperature, we discuss about its potentialities to silicon in optoelectronic applications.

Realization of silicon quantum wires by selective chemical etching and thermal oxidation

Ultra-fine silicon quantum wires with SiO2 boundaries were successfully fabricated by combining SiGe/Si heteroepitaxy, selective chemical etching and subsequent thermal oxidation. The results are observed by scanning electron microscopy. The present method provides a very controllable way to fabricate ultra-fine silicon quantum wires, which is fully compatible with silicon microelectronic technology. As one of the key processes of controlling the lateral dimensions of silicon quantum wires, the wet oxidation of silicon wires has been investigated, self-limiting wet oxidation phenomenon in silicon wires is observed. The characteristic of the oxidation retardation of silicon wires is discussed.

Ultrafine silicon quantum wires fabricated by selective chemical etching and thermal oxidation

Combining SiGe/Si heteroepitaxy, selective chemical etching, and subsequent thermal oxidation, we have successfully fabricated ultrafine silicon quantum wires (SQWRs) with Si/SiO2 interfaces. Experimental result shows that the present method provides a very controllable way to fabricate ultrafine SQWRs, that is completely compatible with silicon microelectronic technology. As one of the key processes of controlling the lateral dimensions of SQWRs, wet oxidation of silicon wires have been investigated. It is found that a self-limiting oxidation phenomenon of silicon wires occurs for wet oxidation. This oxidation retardation characteristic of silicon wires is discussed.

Novel approach for synthesizing of nanometer-sized Si crystals in SiO 2 by ion implantation and their optical characterization

Nanocrystals of Si have been fabricated inside SiO 2 by ion implantation and subsequent vacuum thermal annealing. The microstructure and optical properties of Si implanted layers have been studied by transmission electron microscopy and photoluminescence spectroscopy. The formation of Si nanocrystals after annealing at 1100°C and the growth in average size of nanocrystals with increasing annealing time have been confirmed. Strong visible photoluminescence around 1.7 eV has been achieved in specimens with Si nanocrystals in SiO 2. The shape of the emission spectrum of the photoluminescence is found to be independent of both excitation energy and annealing time. However, the luminescence intensity grows and then decreases as the annealing time increases. Based on these results, we conclude that the photons are absorbed by Si nanocrystals, for which the bandgap energy is modified by the quantum confinement effects, and the emission of photons is not due to direct electron-hole recombination inside Si nanocrystals but is related to defects probably at the interface between Si nanocrystals and SiO 2. The method for the formation of Si nanocrystals inside SiO 2 is fully compatible with silicon microelectronic technology.