| 51. |
- Krishnaraja, Abinaya, et al.
(author)
-
Fabrication of Tunnel FETs demonstrating sub-thermal subthreshold slope
- 2019
-
Conference paper (peer-reviewed)abstract
- Tunnel Field Effect Transistor (TFET), based on band-to-band tunneling, overcomes the thermal limit (subthreshold slope (S) > 60 mV/decade) of the MOSFETs by filtering the high-energy Fermi tail, thereby allowing a substantial reduction of supply voltage and power consumption. Despite the steep slope behavior, TFETs can suffer from ambipolarity wherein carriers tunnel into the channel at both high positive and negative gate voltages. In this work, we demonstrate the fabrication of InAs/InGaAsSb/GaSb vertical nanowire TFET devices and present experimental data showcasing suppressed ambipolarity and a minimum S = 39 mV/decade at Vds=0.05V. The nanowires were grown using MOVPE where the 100nm long InAs drain was n-doped with TESn followed by a 100nm undoped InAs channel and a 100nm/300nm DEZn doped InGaAsSb/GaSb source. After growth, the InAs was selectively digitally etched using citric acid to reduce the channel diameter from 40nm to 25nm. The electrostatics was improved, compared to our previously reported devices, with a gate stack of ALD bilayer of 1nm/3nm Al2O3/HfO2 (EOT~1nm) followed by 30nm sputtered W. To decrease the ambipolar conduction, a gate-drain underlap of approximately 20nm was used which widens the tunnel barrier at the drain junction. Since the gate length is defined by the bottom spacer thickness in vertical transistors, the underlap provides a shorter gate positioned close to the source-channel junction. Thus the new process scheme has improved the slope and reduced the OFF current by one order of magnitude compared to our previous devices [1]. [1] E. Memisevic et al., IEEE Trans.ElectronDevices,vol.64,4746–4751, 2017.
|
|
| 52. |
- Krishnaraja, Abinaya, et al.
(author)
-
Reducing ambipolar off-state leakage currents in III-V vertical nanowire tunnel FETs using gate-drain underlap
- 2019
-
In: Applied Physics Letters. - : AIP Publishing. - 1077-3118 .- 0003-6951. ; 115:14
-
Journal article (peer-reviewed)abstract
- Tunnel Field-Effect Transistors (TFETs) are an emerging alternative to CMOS for ultralow power and neuromorphic applications. The off current (Ioff) and, hence, the subthreshold swing (S) in these devices are limited by ambipolarity, which degrades its capabilities in complementary circuits. Here, we investigate experimentally vertical InAs/InGaAsSb/GaSb nanowire TFETs with gate-drain underlap as a potential solution to avoid ambipolarity and study the temperature dependence of the tunneling current. We compare two different TFET designs, one with an underlap between the gate and drain and the other with an overlap. The introduction of a 25-nm-long underlap region reduced the minimum achievable current Imin from 92 pA/μm to 23 pA/μm by suppressing the ambipolarity and simultaneously improved the minimum S at room temperature from 46 mV/dec to 41 mV/dec at Vds = 0.1 V. We also observe a reduction in the measured on current (Ion) from 0.1 μA/μm in the overlapped device to 0.01 μA/μm in the underlapped device at a drain bias (Vds) = 0.1 V and Ioff = 1 nA/μm. Temperature dependent measurements reveal a potential barrier at the drain junction due to the ungated region at the underlap. We determine a barrier height of 63 meV at Vds = 0.1 V based on thermionic emission combined with a ballistic transport model. Thus, we conclude that gate placement on the drain side is crucial to obtain the low off-currents in TFETs required for ultralow power electronic applications but that the trade-off between Ion and Ioff has to be considered.
|
|
| 53. |
- Krishnaraja, Abinaya, et al.
(author)
-
Tuning of Source Material for InAs/InGaAsSb/GaSb Application-Specific Vertical Nanowire Tunnel FETs
- 2020
-
In: ACS Applied Electronic Materials. - : American Chemical Society (ACS). - 2637-6113. ; 2:9, s. 2882-2887
-
Journal article (peer-reviewed)abstract
- Tunnel field-effect transistors (TFETs) are promising candidates that have demonstrated potential for and beyond the 3 nm technology node. One major challenge for the TFETs is to optimize the heterojunction for high drive currents while achieving steep switching. Thus far, such optimization has mainly been addressed theoretically. Here, we experimentally investigate the influence of the source segment composition on the performance for vertical nanowire InAs/InGaAsSb/GaSb TFETs. Compositional analysis using transmission electron microscopy is combined with simulations to interpret the results from electrical characterization data. The results show that subthreshold swing (S) and transconductance (gm) decrease with increasing arsenic composition until the strain due to lattice mismatch increases them both. The role of indium concentration at the junction is also examined. This systematic optimization has rendered sub-40 mV/dec operating TFETs with a record transconductance efficiency gm/ID = 100 V-1, and it shows that different source materials are preferred for various applications.
|
|
| 54. |
- Larsson, Erik, 1983, et al.
(author)
-
A Comparative Study of the Initial Corrosion of KCl and PbCl2 on a Low-Alloyed Steel
- 2017
-
In: Oxidation of Metals. - : Springer Science and Business Media LLC. - 1573-4889 .- 0030-770X. ; 87:5-6, s. 779-787
-
Journal article (peer-reviewed)abstract
- Heat exchange surfaces in biomass- and waste-fired boilers are exposed to corrosive species due to the considerable amounts of alkali chlorides and PbCl2 which are released during combustion. The corrosivity of alkali chlorides toward superheater alloys exposed at high temperature has been studied extensively. However, at lower material temperatures, i.e., at waterwall conditions, considerably less research has been performed. In order to investigate the effect of small amounts of KCl and PbCl2 during the initial stages of the corrosion attack, a Fe–2.25Cr–1Mo steel was exposed for 24 h in an atmospheres consisting of O2 + H2O + N2 at 400 °C. Both KCl and PbCl2 resulted in an increased corrosion rate compared to the reference. The aim of the present paper is to investigate the influence of KCl and PbCl2 on the initial oxidation of a Fe–2.25Cr–1Mo steel. The work involves a detailed microstructural investigation as well as thermodynamic equilibrium calculations.
|
|
| 55. |
- Larsson, Erik, 1983, et al.
(author)
-
The Influence of KCl and HCl on the High-Temperature Oxidation of a Fe-2.25Cr-1Mo Steel at 400 °C
- 2020
-
In: Oxidation of Metals. - : Springer Science and Business Media LLC. - 1573-4889 .- 0030-770X. ; 93:1-2, s. 29-52
-
Journal article (peer-reviewed)abstract
- The influence of alkali- and chlorine-containing compounds on the corrosion of superheater alloys has been studied extensively. The current paper instead investigates the corrosive effects of KCl and HCl under conditions relevant to waterwall conditions. A low-alloy (Fe-2.25Cr-1Mo) steel was exposed to KCl(s), 500 vppm HCl(g) and (KCl + HCl) in the presence of 5%O2 and 20% H2O at 400 °C. The results indicate that alloy chlorination by KCl occurs by an electrochemical process, involving cathodic formation of chemisorbed KOH on the scale surface and anodic formation of solid FeCl2 at the bottom of the scale. The process is accompanied by extensive cracking and delamination of the iron oxide scale, resulting in a complex, convoluted scale morphology. Adding 500 vppm HCl to the experimental environment (KCl + HCl) initially greatly accelerated the formation of FeCl2 at the scale/alloy interface. The accelerated alloy chlorination is attributed to HCl reacting with KOH at the scale surface, causing the cathodic process to be depolarized. A rapid slowing down of the rate of chlorination and corrosion in KCl + HCl environment was observed which was attributed to the electronically insulating nature of the FeCl2 layer which forms at the bottom of the scale, disconnecting the anodic and cathodic regions.
|
|
| 56. |
- Lindahl, Mattias, 1971-, et al.
(author)
-
Industrial cleaning with Qlean Water : a case study of printed circuit boards
- 2013
-
In: Journal of Cleaner Production. - : Elsevier BV. - 0959-6526 .- 1879-1786. ; 47, s. 19-25
-
Journal article (peer-reviewed)abstract
- Many manufacturing companies are looking for ways to substitute environmentally problematic cleaning methods for surface treatments with more environmentally friendly ones. In this paper, one potential solution is described. The Qlean method, based on cleaning with highly pure water (in this paper defined as Qlean Water), is a novel cleaning method. This method, now utilized at one plant at a leading major international electronic company, has substituted previous chemical-based methods for cleaning printed circuit boards prior to lacquering. This paper presents, based on that company's primary data, a comparative study using environmental analysis and economic life cycle cost review between cleaning with Qlean Water and conventional cleaning. The focus is on the environmental and economic performance of the two alternatives. The conclusion is that Qlean Water offers both a significant economic and environmental cost reduction and a better product. This is the case even though all identified economic benefits derived from using Qlean Water, e.g. that the quality and technical lifetime have been extended for the printed circuit boards with the Qlean Water cleaning method, are not considered in the economic analysis.
|
|
| 57. |
- Lindgren, Stig-Åke, 1950, et al.
(author)
-
Coverage-dependent frequency for Li-atom vibrations on Cu(111)
- 1996
-
In: Physical Review B. - 2469-9969 .- 2469-9950. ; 54:15, s. 10912 - 10916
-
Journal article (peer-reviewed)abstract
- Electron-energy-loss spectra recorded for monolayer amounts of Li adsorbed on Cu(111) show a loss peak associated with Li vibrations perpendicular to the substrate. The loss energy shifts from 38 meV at low coverage to 43 meV at 0.3 ML and remains constant for coverages between 0.3 and 0.5 ML. The loss intensity passes a maximum at a Li coverage of 0.15 ML and gradually decreases such that it is difficult to resolve a loss peak at coverages above 0.5 ML. The high loss energy indicates that the adatom resides on the surfaces rather than in substitutional sites. The frequency shift is much too large to be explained by dipole-dipole interactions. The above results are obtained with the evaporation source loaded with the natural Li isotope mixture (92.6% 7Li, 7.4% 6Li). Measurements with 6Li show that the increase of the vibration frequency with increasing coverage is not an isotope effect.
|
|
| 58. |
|
|
| 59. |
- Mattsson, Jan Erik, et al.
(author)
-
Halmaska i kretslopp
- 2010
-
In: LTJ-fakultetens faktablad.
-
Other publication (pop. science, debate, etc.)abstract
- Analyser på vetehalm från fyra platser i Skåne samt danska erfarenheter från återföring av halmaska i stor skala visar att halmaska kan användas som gödselmedel på åkermark och klassas som ett kaliumgödselmedel med viss fosfor- och kalkverkan. Med halmbärgning och halmeldning bortförs växtnäringen i halmen från åkermarken, men den finns i halmaskan, förutom kvävet som följer med rökgaserna. Askan innehåller dock även andra ämnen som tagits upp av växten, t. ex. kadmium. Kadmiumhalten var högre i vetehalm från gårdar med högre kadmiumhalt i matjorden. Om endast bottenaskan efter förbränning av halm används som gödselmedel, bör metoder utvecklas för utvinning av kalium ur flygaskan, eftersom den innehåller hälften av halmaskans kalium. Fortsatta studier bör inriktas på växttillgängligheten hos kalium, fosfor och kadmium i halmaska samt utvärdering av ny teknik för spridning av små mängder halmaska per hektar
|
|
| 60. |
- Memisevic, Elvedin, et al.
(author)
-
Impact of Band-Tails on the Subthreshold Swing of III-V Tunnel Field-Effect Transistor
- 2017
-
In: IEEE Electron Device Letters. - 0741-3106. ; , s. 1661-1664
-
Journal article (peer-reviewed)abstract
- We present a simple model to evaluate the sharpness of the band edges for tunnel field-effect transistors by comparing the subthreshold swing and the conductance in the negative differential resistance region. This model is evaluated using experimental data from InAs/InGaAsSb/GaSb nanowire tunnel-field effect transistors with the ability to reach a subthreshold swing well below the thermal limit. A device with the lowest subthreshold swing, 43 mV/decade at 0.1 V, exhibits also the sharpest band-edge decay parameter E0 of 43.5 mV although in most cases the S<
|
|
