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GaSb nanowire transistors with process induced strain

Winqvist, Edvin LU (2017) FYSM60 20171
Department of Physics
Combustion Physics
Abstract
With the constant downscaling of Si transistors reaching its limits, other alternatives have been actively researched the past decades. Group III-V semiconductors are excellent materials with generally high carrier mobilities that can replace Si in transistors. Strain has been used for some years to improve silicon technology, and it can also be applied to III-V materials to make them perform even better. In this work, GaSb nanowire transistors were strained using PECVD to deposit a stressing film of Si3N4 and the effects on the electrical characteristics investigated.

The deposited films ranged between thicknesses of 40-104 nm, with stresses in the range 300-2000 MPa. Raman spectroscopy measurements showed a strain in the nanowires up... (More)
With the constant downscaling of Si transistors reaching its limits, other alternatives have been actively researched the past decades. Group III-V semiconductors are excellent materials with generally high carrier mobilities that can replace Si in transistors. Strain has been used for some years to improve silicon technology, and it can also be applied to III-V materials to make them perform even better. In this work, GaSb nanowire transistors were strained using PECVD to deposit a stressing film of Si3N4 and the effects on the electrical characteristics investigated.

The deposited films ranged between thicknesses of 40-104 nm, with stresses in the range 300-2000 MPa. Raman spectroscopy measurements showed a strain in the nanowires up to 0.5%. The effect on the threshold voltage from the Si3N4 films containing positive charges made it challenging to separate the effects from this and the effects from strain. All samples exhibited a reduction in current but a signicant increase in the on/off-ratio, making the strained devices turn off much better than untreated devices, with an on/off-ratio increase of up to 70 times observed. The results obtained here show that this method of process induced strain could see uses in order to reduce power consumption. (Less)
Popular Abstract (Swedish)
“Om bilar hade utvecklats lika snabbt som datorprocessorer skulle de köra i 760 000 km/h, köra 100 km på enbart 2.4 ml bensin, och kosta 30 öre” hävdar Paul Ottelini, tidigare VD för Intel som är planetens största utvecklare och tillverkare av processorer.

En processor är den enhet i din dator eller telefon som utför alla instruktioner och beräkningar som program kräver. Processorer idag innehåller flera miljarder transistorer, som är den viktigaste byggstenen i de flesta elektroniska komponenter. Det är en makalös prestation som gjorts inom utvecklingen av transistorer de senaste 50 åren som lett till den prestanda vår teknologi har idag.

En transistor uppför sig som en lampknapp, som antingen kan slås av eller på mer är en miljard... (More)
“Om bilar hade utvecklats lika snabbt som datorprocessorer skulle de köra i 760 000 km/h, köra 100 km på enbart 2.4 ml bensin, och kosta 30 öre” hävdar Paul Ottelini, tidigare VD för Intel som är planetens största utvecklare och tillverkare av processorer.

En processor är den enhet i din dator eller telefon som utför alla instruktioner och beräkningar som program kräver. Processorer idag innehåller flera miljarder transistorer, som är den viktigaste byggstenen i de flesta elektroniska komponenter. Det är en makalös prestation som gjorts inom utvecklingen av transistorer de senaste 50 åren som lett till den prestanda vår teknologi har idag.

En transistor uppför sig som en lampknapp, som antingen kan slås av eller på mer är en miljard gånger per sekund. Genom att kombinera transistorer som är antingen av eller på kan processorn utföra komplicerade beräkningar snabbt.

Transistorer har sedan länge varit tillverkade av kisel, vilket är ett ämne med bra elektriska egenskaper, men det har främst blivit använt tack vare dess rikliga tillgång på jorden, eftersom det utvinns från sand, vilket även gör kisel väldigt billigt. Utvecklingen av transistorer har mest skett genom att minska storleken på dem vilket gör dem snabbare, men de är numera så pass små att detta inte är möjligt. Därför sker det mycket forskning kring andra ämnen som kan ersätta kisel, eller att hitta andra metoder som kan förbättra transistorerna. En sådan metod som använts i flera år på kiselprodukter är att belasta transistorerna så de trycks ihop. Det har visat sig att om ett ämne som kisel trycks ihop så att atomerna hamnar närmre varandra, kan dess elektriska egenskaper förbättras avsevärt.

I det här arbetet har denna teknik använts på nanotrådar av galliumantimonid. En nanotråd är ett trådformat objekt så litet att det skulle behöva ligga flera miljoner trådar intill varandra för att du skulle kunna upptäcka dem med blotta ögat. Galliumantimonid är ett av de ämnen som kisel kan bytas mot, det är dock mycket dyrare. Nanotrådarna som användes låg på en öppen yta, och ett tunt lager av kiselnitrid deponerades ovanpå. Detta lager drar ihop allting under sig. Tänk dig att du sträcker ut ett plåster innan du fäster det över ett sår, det kommer då vilja dra ihop sig självt samt huden det är fäst på. På ett liknande sätt drar kiselnitriden ihop nanotrådarna.

Resultaten som erhölls i detta projekt var av blandad natur. Optiska mätningar visade att filmen kunde användas för att belasta trådarna, men det upptäcktes ingen större förbättring med ökad belastning, och det kan nog vara så att andra metoder är bättre för att sträcka ut eller trycka ihop transistorerna. Ett positivt resultat var att närheten av kiselnitriden gjorde så att strömmen genom transistorerna var lättare att stänga av. I vanliga fall går det inte att stänga av transistorer helt, utan de läcker alltid lite ström. Det visade sig i detta projekt att denna läckström blev upp till hundra gånger lägre när nanotrådarna var i kontakt med kiselnitriden. (Less)
Popular Abstract
"If cars had developed as fast as computer processors they would go at 760 000 km/h, drive 100 km on only 2.4 ml gas, and cost 3 cents" claims Paul Ottelini, former CEO of Intel which is the world leading developer and manufacturer of processors.

A processor is the unit in your phone or computer that performs all the instructions or calculations that programs require. Processors today consist of billions of transistors, which is the most important building block in most electronic components. It is an amazing accomplishment that's been done in the development of transistors over the past 50 years that has led to the performance of our technology today.

A transistor behaves as a switch, that can be turned either on or off more than a... (More)
"If cars had developed as fast as computer processors they would go at 760 000 km/h, drive 100 km on only 2.4 ml gas, and cost 3 cents" claims Paul Ottelini, former CEO of Intel which is the world leading developer and manufacturer of processors.

A processor is the unit in your phone or computer that performs all the instructions or calculations that programs require. Processors today consist of billions of transistors, which is the most important building block in most electronic components. It is an amazing accomplishment that's been done in the development of transistors over the past 50 years that has led to the performance of our technology today.

A transistor behaves as a switch, that can be turned either on or off more than a billion times per second. By combining transistors that are turned on or off, the processor can perform complicated tasks fast.

Transistors have since long been made out of silicon, which is a material with good electrical properties, but it has mainly been used due to its ample availability on earth, since it is extracted from sand, which also makes silicon very cheap. The development of transistors has mostly been done by reducing their size which makes them faster, but they are now so small that this is no longer possible. Therefore, much research is taking place around other materials that could replace silicon, or finding other methods that can enhance transistors further. One such method that has been used on the market for some years now is straining the silicon in transistors. It has been found that by straining a material so that its atoms are closer together or further apart can considerably improve its electrical properties.

In this work, strain has been used on nanowires of gallium antimonide. A nanowire is a wireshaped object so small that it would require a million adjacent wires to be spotted with the naked eye. Gallium antimonide is one of the materials that could replace silicon, although it is much more expensive. The nanowires that were used were lying on an open surface, with a thin layer of silicon nitride deposited on top. This layer pulls together everything beneath it. Imagine if you stretch a band-aid before putting it on a wound, it would try to pull itself back to its normal state, and also pull on your skin beneath it. In a similar way the nanowires are strained by the silicon nitride layer.

The results obtained in this project were of mixed nature. Optical measurements showed that the film could be used to strain the wires, but no big enhancement was found with increased strain, which could mean that other straining methods are probably better. A positive result was that the vicinity of the silicon nitride layer made the current through the transistors easier to turn off. A transistor is normally never completely turned off, there is always a small leakage of current. It was shown in this project that this leakage current was reduced up to a hundred times when the wires were in contact with the silicon nitride. (Less)
Please use this url to cite or link to this publication:
author
Winqvist, Edvin LU
supervisor
organization
course
FYSM60 20171
year
type
H2 - Master's Degree (Two Years)
subject
keywords
GaSb, gallium, antimonide, nanowire, transistor, strain, physics, thesis
language
English
id
8910574
date added to LUP
2017-06-08 10:11:18
date last changed
2017-06-08 10:11:18
@misc{8910574,
  abstract     = {With the constant downscaling of Si transistors reaching its limits, other alternatives have been actively researched the past decades. Group III-V semiconductors are excellent materials with generally high carrier mobilities that can replace Si in transistors. Strain has been used for some years to improve silicon technology, and it can also be applied to III-V materials to make them perform even better. In this work, GaSb nanowire transistors were strained using PECVD to deposit a stressing film of Si3N4 and the effects on the electrical characteristics investigated.

The deposited films ranged between thicknesses of 40-104 nm, with stresses in the range 300-2000 MPa. Raman spectroscopy measurements showed a strain in the nanowires up to 0.5%. The effect on the threshold voltage from the Si3N4 films containing positive charges made it challenging to separate the effects from this and the effects from strain. All samples exhibited a reduction in current but a signicant increase in the on/off-ratio, making the strained devices turn off much better than untreated devices, with an on/off-ratio increase of up to 70 times observed. The results obtained here show that this method of process induced strain could see uses in order to reduce power consumption.},
  author       = {Winqvist, Edvin},
  keyword      = {GaSb,gallium,antimonide,nanowire,transistor,strain,physics,thesis},
  language     = {eng},
  note         = {Student Paper},
  title        = {GaSb nanowire transistors with process induced strain},
  year         = {2017},
}