Combinatorial material synthesis applied to Ge-Sb-Te based phase-change materials [Elektronische Ressource] / vorgelegt von Han-Willem Wöltgens

Han-Willem Wöltgens

Sujets

• Physik

Informations

• Publié par: rheinisch-westfalischen_technischen_hochschule_-rwth-_aachen
• Publié le: 01 janvier 2003
• Nombre de lectures: 14
• Langue: English
• Poids de l'ouvrage: 11 Mo

Extrait

Combinatorial material synthesis
applied to Ge-Sb-Te based
phase-change materials
Von der Fakultät für Mathematik, Informatik und Naturwissen-
schaften der Rheinisch-Westfälischen Technischen Hochschule Aa-
chen zur Erlangung des akademischen Grades eines Doktors der
Naturwissenschaften genehmigte Dissertation
Vorgelegt von
Diplom-Physiker
Han-Willem Wöltgens
aus Heerlen/Niederlande
Berichter: Universitätsprofessor Dr. M. Wuttig
Universitätsprofessor Dr. J. Geurts
Tag der mündlichen Prüfung: 16. Mai 2003
Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek online verfügbar.Inhaltsverzeichnis
1 Introduction 1
1.1 phase-change recording materials . . . . . . . . . . . . . . . . . . . . . . . 5
1.2 Combinatorial materials science . . . . . . . . . . . . . . . . . . . . . . . . 6
2 Basicemissionlawsforthermalevaporationandthetheoryofcrystallisation 11
2.1 The Hertz-Knudsen equation . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2 The cosine law of emission . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.3 Thickness profiles from basic emission laws . . . . . . . . . . . . . . . . . . 14
2.4 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.5 The deposition of alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.6 Lateral stoichiometry distribution function . . . . . . . . . . . . . . . . . . 24
2.7 Crystallisation Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.8 The Peierls Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3 Experimental methods & procedures 41
3.1 Verification of the thickness gradients . . . . . . . . . . . . . . . . . . . . . 41
3.2 Stoichiometry measurement methods . . . . . . . . . . . . . . . . . . . . . 45
3.3 Screening tools, static tester . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.4 Methods for single stoichiometry samples . . . . . . . . . . . . . . . . . . . 51
4 The experimental setup 79
4.1 Thermal evaporation from Knudsen cells . . . . . . . . . . . . . . . . . . . 79
4.2 The ultra high vacuum chamber . . . . . . . . . . . . . . . . . . . . . . . . 85
4.3 Quartz crystal oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
4.4 Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
4.5 Thickness profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
◦4.6 The influence of evaporation under 45 on film structure . . . . . . . . . . 96
5 Results I: the evaporants Ge, Sb, Te and GeTe 105
5.1 Germanium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
5.2 Antimony . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
5.3 Tellurium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
IInhaltsverzeichnis
5.4 Germanium-Telluride, GeTe . . . . . . . . . . . . . . . . . . . . . . . . . . 114
6 Results II: combinatorial samples 127
6.1 The compound Sb Te . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1282
6.2 The compound Sb Te . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1312 3
6.3 The compound Ge Sb Te . . . . . . . . . . . . . . . . . . . . . . . . . . . 1362 2 5
6.4 The compound Ge SbTe . . . . . . . . . . . . . . . . . . . . . . . . . . . 1554 5
6.5 The compound GeSb Te . . . . . . . . . . . . . . . . . . . . . . . . . . . 1762 4
7 Summary and suggestions for future work 197
7.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
7.2 Suggestions for future work . . . . . . . . . . . . . . . . . . . . . . . . . . 203
A Appendix 205
A.1 Phase Diagram GeSbTe . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
B Literaturverzeichnis 207
C Abbildungsverzeichnis 217
D Tabellenverzeichnis 225
E Acknowledgement 227
F Lebenslauf 229
Inhaltsverzeichnis
II1 Introduction
Much work has been devoted in the last years to optical recording technologies to respond
to increasing demand for higher storage capacities and data transfer rates. The currently
appliedre-writableopticalrecordingtechnologiesarebasedonphase-changeandmagneto-
optical technologies. In phase-change optical recording technology, micron sized areas of
the active layer are reversibly switched between amorphous and crystalline states. On
the contrary, in magneto-optical recording the magnetisation direction of perpendicularly
magnetised domains is switched in a magnetic thin film. Phase-change recording has
advanced remarkably in the last ten years to become a mature technology for re-writable
optical data storage systems. Furthermore, there are initiatives to implement non-volatile
random access memories based on phase-change materials. Besides optical data storage
applications also magnetic data storage media, like hard drives, are aiming at the mass
datastoragemarket.Hence,beforewetakeacloserlookatphase-changeopticalrecording,
a brief review of the history of magnetic storage will be given.
In the early sixties, Gordon Moore observed that the areal density for magnetic sto-
rage duplicates every 18 months. Figure 1.1 illustrates the history for the last 18 years
and the road map of the areal density. Still the areal density is still increasing rapidly
following Moore’s law even after all those years. In November 2002 Seagate Technology
2demonstrated 100Gbit/in by perpendicular recording. This has also enabled record data
rates of up to 125 MB per second. As the areal density growth rate of current longitudinal
recording begins to slow down, perpendicular recording appears best-positioned to keep
pace with the world’s growing data storage needs, with the potential for far higher densi-
ty levels over time than what could otherwise be achieved. With this technique they can
surpassthesuper-paramagneticeffect,whichwasuptonowthefinalfrontierformagnetic
storage applications. Perpendicular recording arranges the magnetic bits vertically on the
surface of the disc, enabling the head to record and read more information per unit area.
Perpendicular recording breaks new ground because today’s disc drives use traditional
longitudinal recording, where the bits are horizontally arranged on the disc and therefo-
re also require more surface area to store information. They even project perpendicular
recording to achieve areal densities as high as one terabit per square inch for the year
2010 (DataStoreX, 2002).
The development of the data transfer rate is illustrated in figure 1.2. The data transfer
rate increases similar to the areal density very rapidly. Nowadays, the data transfer rate
is approximately 100 MBytes/s, which implies that the time to write, erase, and read a
bit is approximately 1 ns. The data transfer rate increased the last decade with 40% a
11 Introduction
3
10
2
Demo: 100 Gb/in
perpendicular recording
2
10 2
Demo: 35 Gb/in
2
Demo: 20.4 Gb/in
1
10
2
Demo: 2.5 Gb/in Areal Density Record
2 for Tape Storage
Demo: 1 Gb/ in0 210 DVD-RAM: 3.6 Gb/in
2
CD: 1.0 Gb/in
-1
10
-2 Magnetic Storage10
Optical Storage
-3
10
1985 1990 1995 2000 2005 2010
year of introduction
Abbildung 1.1: Road map of the areal data density.
year. Hence, we would expect a data transfer rate of 1 TBytes/s within now and the next
ten years, which implies write, erase and read times of less then 0.1 ns.
In the case of optical data storage applications the prospects are not that optimistic.
Hence, in order for optical data storage applications to keep pace with the standards
set by magnetic recording something crucial has to occur. In order for the phase-change
recording technology to remain competitive in the long term efforts should be directed to
identify the key mechanisms and properties in the class of phase-change materials.
In the next section, a brief discussion on the principle of phase-change optically recor-
ding works will be presented. Then a brief history of materials currently used by industry
uptonowwillbegiven.Usingthisknowledge,aselectionofcriteriaforcandidatematerials
can be postulated. Based on these criteria we demonstrate an approach, how new mate-
rials can be prepared and tested for optical data storage application much more quickly
than standard methods.
Figure 1.3(a) shows the basic laser pulse strategy to write, erase, and read data to and
from a re-writable optical disk. A short intense laser pulse is used to locally melt the
crystalline material and subsequently cool the region rapidly. The resulting amorphous
2
2
areal density (Gb/in )1 Introduction
3
10
2
10
110
1990 1995 2000 2005
Availability year
Abbildung 1.2: Development of the data transfer rate for magnetic hard disk drives.
region is then the bit. A pulse, which heats the bit above the crystallisation temperature,
is used to erase the bit. Finally, a moderate pulse reads out the reflectance and detects
the actual state of the bit. In figure 1.3(b) a time-temperature-transformation diagram
is shown, which represents the transformed fraction of an iso-thermal phase transition
as function of the time and temperature. The yellowish region represents the melt, while
the blue and the red regions denote the amorphous structure and crystall