Freek E. Prins

Reduction of charge-transport characteristics of SiGe dot floating gate memory device with ZrO/sub 2/ tunneling oxide

We have demonstrated the effects of charging voltage and the charge retention characteristics in silicon-germanium dots with ZrO/sub 2/ tunneling oxide. Using the ZrO/sub 2/ high-k dielectric tunneling oxide, we achieved a low write voltage and improved retention time as compared to the SiGe dots with a SiO/sub 2/ tunneling oxide. The discharge behavior of the ZrO/sub 2/ device is similar to that of Si dots embedded in SiO/sub 2/ in terms of a logarithmic charge decay. This demonstrates that the SiGe dots with ZrO/sub 2/ tunneling oxide can be used to replace SiGe dots with SiO/sub 2/ tunneling oxide as the floating gate in EEPROMs and have a high potential for further scaling of floating-gate memory devices.

Growth of germanium quantum dots on different dielectric substrates by chemical-vapor deposition

The growth of Ge quantum dots on various nitrided oxides has been achieved by ultra-high-vacuum chemical-vapor deposition with GeH4 gas at temperatures between 550 and 650 °C. The characteristics of the Ge dots were investigated using atomic-force microscopy, Auger electron spectroscopy, and x-ray photoelectron spectroscopy in order to find the mechanism of the Ge dot formation. On N2O-annealed nitrided oxide films, we obtained Ge dots with height and diameters of 3.2 and 11 nm, respectively. No Ge dots were formed on surfaces of other dielectric substrates at 550 °C. From our experimental results, we suggest that the surface of N2O-annealed nitrided oxide contains a large amount of defects such as dangling bonds, which act as Ge nucleation sites. This is further confirmed by studying the growth kinetics and the influence of in situ annealing of the samples.The growth of Ge quantum dots on various nitrided oxides has been achieved by ultra-high-vacuum chemical-vapor deposition with GeH4 gas at temperatures between 550 and 650 °C. The characteristics of the Ge dots were investigated using atomic-force microscopy, Auger electron spectroscopy, and x-ray photoelectron spectroscopy in order to find the mechanism of the Ge dot formation. On N2O-annealed nitrided oxide films, we obtained Ge dots with height and diameters of 3.2 and 11 nm, respectively. No Ge dots were formed on surfaces of other dielectric substrates at 550 °C. From our experimental results, we suggest that the surface of N2O-annealed nitrided oxide contains a large amount of defects such as dangling bonds, which act as Ge nucleation sites. This is further confirmed by studying the growth kinetics and the influence of in situ annealing of the samples.

Investigation of the modification mechanism induced by a scanning tunneling microscope on YBa2Cu3O7−δ

The scanning tunneling microscope (STM) was used to modify wires of the high temperature superconductor YBa2Cu3O7−δ (YBCO) which had been fabricated by electron beam lithography in order to simulate realistic conditions of a fabrication process. The linewidth of the structures generated with the STM was well below 50 nm. For a deeper understanding of the mechanism responsible for the STM-induced modifications, the experiments were performed under ambient conditions, in ultrahigh vacuum, carbon dioxide atmosphere, and nitrogen atmosphere. Results indicate that both water and carbon dioxide are essential for the modification process on the YBCO wires. This suggests that the modification mechanism is based on a water-mediated electrochemical decomposition of YBCO in the field of the STM tip.

Modification of YBa2Cu3O7−δ wires using a scanning tunneling microscope: Process and electrical transport effects

Wires of the high temperature superconductor YBa2Cu3O7−δ (YBCO) were fabricated by electron beam lithography and were subsequently modified further on a sub-100 nm scale using the scanning tunneling microscope (STM). The process responsible for this modification has been shown to be field enhanced corrosion of the YBCO surface in the presence of CO2 and H2O. The intention of this work is to investigate the effect of the STM induced modifications on the electrical transport behavior of the YBCO wires with current–voltage characteristics (CVCs) measured at 77 and 4.2 K. Different types of CVCs can be distinguished, depending on the size of the cut into the wire generated by the STM. The measured characteristics will be explained by thermal self-heating at locations of the wire induced by the STM. Thus, the STM modifications initiate thermal domains in the wire where the Joule heat emission generated at sufficient high current values raise the temperature of the wire above its critical temperature. Furthermo...

Charge retention characteristics of SiGe quantum dot flash memories

For application to nonvolatile memory devices, a long retention time is most important. Recent efforts on alternate high-K gate dielectric materials replacing silicon dioxide in complementary metal-oxide-semiconductor (CMOS) technology have demonstrated a higher /spl epsiv/ values, reduced leakage, improved resistance to boron diffusion, and better reliability characteristics. In this paper we present the charge retention characteristics of SiGe nanocrystals embedded in ZrO/sub 2/ using a TaN/ZrO/sub 2//Si MIS. The devices show improved retention characteristics and have a high potential for further scaling of EEPROM cells.

An asymmetric Si/Si1−xGex channel vertical p-type metal-oxide-semiconductor field-effect transistor

Abstract In this study, we discuss a vertical p-type metal-oxide-semiconductor field-effect transistor device structure with an asymmetric Si/Si1−xGex deep submicron (100 nm) channel. The source and source end of the channel are made of Si while rest of the channel and the drain are made of strained Si1−xGex. Compared with conventional Si device, the drive current of this asymmetric channel device is improved due to high electric field near the source end, high pinchoff voltage and high hole mobility in the strained Si1−xGex layer. The short channel effects and punchthrough are not degraded because the source and channel junction is made of Si, instead of strained Si1−xGex which has a smaller band gap.

Vertical p-type high-mobility heterojunction metal–oxide–semiconductor field-effect transistors

We have fabricated a vertical p-channel metal–oxide–semiconductor field-effect transistor called high-mobility heterojunction transistor (HMHJT). Compared with a Si control device, reduced short channel effects, reduced floating body effect, and high drive current have been achieved with this device structure. A SiGe/Si heterojunction barrier at the source/bulk junction suppresses drain induced barrier lowering and bulk punchthrough, which are significant problems for sub-100 nm devices. A SiGe source also helps to reduce the charge built-up in the floating body. The higher mobility in a strained SiGe channel and the absence of a hetero-barrier between the source and channel result in higher drive current. The fabricated HMHJT has a 60% higher drive current at VDS=VGS−VT=−1.6 V, and a 70× lower off-state leakage current at VDS=−1.6 V and VGS=0.0 V, compared with the Si control device.

Performance enhancement in vertical sub-100 nm nMOSFETs with graded doped channels

Graded channel doping in vertical sub-100 nm nMOSFETs was investigated in this study. Conventional single step ion implantation was used to form the asymmetric, graded doping profile in the channel. No large-angle-tilt implant was needed. The device fabrication was compatible with conventional Si CMOS technology. In a graded doped channel, with the higher doping level in the source end of the channel, drain induced barrier lowering and off-state leakage current were reduced significantly. In addition, lower longitudinal electric field in the drain end can be achieved without lightly doped drain (LDD), and hot carrier effects were reduced substantially with this device.

Si/sub 1-x/Ge x channel vertical PMOSFET with asymmetric Ge profile

Describes a vertical PMOSFET with an asymmetric Si/Si/sub 1-x/Ge/sub x/ channel . On the source side, the channel is made of Si, so the short channel performance is not degraded compared with a Si device. The rest of the channel is made of strained Si/sub 1-x/Ge/sub x/. and we still can take advantage of the high hole mobility in the strained Si/sub 1-x/Ge/sub x/ layer. The energy step in the channel increases the lateral electric field near the source and helps with carrier injection from the source to the channel. Ultra-high vacuum chemical vapor deposition (UHV-CVD) was used to grow the device layers with in situ doping.

The characterization of initial growth of polycrystalline silicon germanium films on zirconium oxide

In this study, the initial growth characteristics of a SiGe film realized by ultrahigh-vacuum chemical vapor deposition (UHV CVD) using GeH 4 and Si 2 H 6 on high- K gate oxide , ZrO 2 , has been investigated in the temperature range from 475°C to 550°C. The influence of surface reactions on growth characteristics such as the incubation of growth, roughness of the SiGe layer, and the interface reaction of the SiGe film with ZrO 2 were studied using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). From our analysis we conclude that ZrO 2 reacts with Si and forms zirconium silicide in the temperature range between 500°C and 550°C. The surface roughness of amorphous SiGe layers increase from 0.5nm to 1.5nm by increasing Ge content from 0.1 to 0.3. A further increase of surface roughness is observed from less than 1nm to 5nm as SiGe layer transitions from an amorphous to a poly crystalline layer.