Universal Mobility Research Articles

Electron mobility enhancement in strained-Si n-MOSFETs fabricated on SiGe-on-insulator (SGOI) substrates

We demonstrate electron mobility enhancement in strained-Si n-MOSFETs fabricated on relaxed Si/sub 1-x/Ge/sub x/-on-insulator (SGOI) substrates with a high Ge content of 25%. The substrates were fabricated by wafer bonding and etch-back utilizing a 20% Ge layer as an etch stop. Epitaxial regrowth was used to produce the upper portion of the Si/sub 0.75/Ge/sub 0.26/ and the surface strained Si layer. Large-area strained-Si n-MOSFETs were fabricated on this SGOI substrate. The measured electron mobility shows significant enhancement over both the universal mobility and that of co-processed bulk-Si MOSFETs. This SGOI process has a low thermal budget and thus is compatible with a wide range of Ge contents in Si/sub 1-x/Ge/sub x/ layer.

Relaxed Silicon-Germanium on Insulator (SGOI)

AbstractWe have fabricated high quality SGOI substrates and demonstrated high mobility enhancement in strained-Si MOSFET's fabricated on the relaxed SGOI substrates with a Ge content of 25%. The substrates were fabricated by wafer bonding. The initial relaxed Si1−xGex layers were grown on Si donor substrates by a graded epitaxial growth technology using ultrahigh vacuum chemical vapor deposition (UHVCVD). The SiGe wafers were then bonded to oxidized silicon handle wafers. Two different approaches have been developed to fabricate SGOI substrates: an etch-back process utilizing a 20% Ge layer as a natural etch stop, and a hydrogen-induced wafer delamination process using H+ implantion. The resultant SiGe film quality was compared among the different approaches. Large-area strained-Si MOSFET's were then fabricated on the SGOI substrates. Epitaxial regrowth was used to produce the upper portion of the relaxed SiGe and the surface strained Si layer. The measured electron mobility shows significant enhancement over both the universal mobility and that of co-processed bulk-Si MOSFET's. This SGOI process has a low thermal budget and thus is compatible with a wide range of Ge contents in Si1−xGex layer.

Electron and hole mobility enhancement in strained-Si MOSFET's on SiGe-on-insulator substrates fabricated by SIMOX technology

We have newly developed strained-Si MOSFET's on a SiGe-on-insulator (strained-SOI) structure fabricated by separation-by-implanted-oxygen (SIMOX) technology. Their electron and hole mobility characteristics have been experimentally studied and compared to those of control SOI MOSFET's. Using an epitaxial regrowth technique of a strained-Si film on a relaxed-Si/sub 0.9/Ge/sub 0.1/ layer and the conventional SIMOX process, strained-Si (20 nm thickness) layer on fully relaxed-SiGe (340 nm thickness)-on-buried oxide (100 nm thickness) was formed, and n-and p-channel strained-Si MOSFET's were successfully fabricated. For the first time, the good FET characteristics were obtained in both n-and p-strained-SOI devices. It was found that both electron and hole mobilities in strained-SOI MOSFET's were enhanced, compared to those of control SOI MOSFET's and the universal mobility in Si inversion layer.

The long and short of channel length

In this article, the powerful shift-and-ratio method proposed by Taur of IBM Corp. [1992] is used to accurately determine effective channel length and mobility of deep-submicron devices. We show that the extracted low field mobility of a short-channel device as a function of gate voltage is consistent with that of a long-channel device. Since in the BSIM3v3.2 industrial standard model a universal low field mobility is used for devices of various sizes, the shift-and-ratio method is particularly suitable for determining accurate effective channel length that leads to a consistent mobility value.

Implications of dopant-dependent low-field mobility and band gap narrowing on the bipolar device performance

Band gap narrowing is one of the crucial heavy-doping effects to be considered for bipolar devices. We present a new band gap narrowing model which considers the semiconductor material and the dopant species for arbitrary finite temperatures. As the minority carrier mobility is of considerable importance for modeling advanced n-p-n bipolar transistors, we implemented the new universal low field mobility model [1] in MINIMOS-NT [2]. This model distinguishes between majority and minority electron mobilities on one hand, and between different dopant species on the other hand, both as a function of temperature and dopant concentration. This unified treatment is especially useful for accurate device simulation. As a particular example we present the results for SiGe HBT.

Quantum Brownian motion in a periodic potential and the multichannel Kondo problem

We study the motion of a particle in a periodic potential with Ohmic dissipation. In $D=1$ dimension it is well known that there are two phases depending on the dissipation: a localized phase with zero temperature mobility $\ensuremath{\mu}=0$ and a fully coherent phase with $\ensuremath{\mu}$ unaffected by the periodic potential. However, for nonsymmorphic lattices with $Dg1$, such as the honeycomb lattice, there is an intermediate phase with a universal mobility ${\ensuremath{\mu}}^{*}$. This intermediate phase is relevant to resonant tunneling experiments in strongly coupled Coulomb-blockade structures as well as multichannel Luttinger liquids. We relate this problem to the Toulouse limit of the $D+1$ channel Kondo problem, which allows us to compute ${\ensuremath{\mu}}^{*}$ exactly using results known from conformal field theory.

Public health versus public policy? An appraisal of British urban transport policy

The most visible aspect of the relationship between transport and health is in the realm of road traffic accidents (RTAs). But the effects of transport policy upon the public health are much wider-ranging. They include exacerbation of social and health inequalities, separation from directly health-protective amenities and social isolation, as well as health damage by physico-chemical pollution. It is arguable that these factors may account for more years of life lost annually than do RTAs. The current focus on accident reduction as the sole means of avoiding adverse health effects of transport distracts attention from the wide health erosive effects of road traffic. Universal mobility and accessibility, independent of the car, is required for public health protection and advancement, since private transport carries many external, and poorly recognised health costs.

Erfahrungen mit der Bader-Leuchte

First experiences with the new lighting system are presented. It consists of a halogen lens projector which is suspended on an entirely new tripod in a fully floating manner allowing universal mobility. The Bader light replaces the frontal mirror in the operating room and with the outpatient work. Because of its outstanding light quality and excellent handling there is no lack at all of the frontal mirror. It is surprising that such a light has been developed as late as now since the facilitation of work through the relief of the vertebral spine from tripod functions is remarkable.