Synthesis of Silicon nanowires for sensor nanowires for sensor applications Anne Claire Salaün Anne - Claire Salaün Nanowires Team Laurent Pichon (Pr), Laurent Pichon (Pr), Régis Rogel (Ass.Pr), Anne-Claire Salaün (Ass. Pr) CMC2 - November 25, 2010 - Barcelona, Spain 1111 FRONTIER-2009, Nov 29-Dec 3, 2009, Sendai, Japan Ph-D positions: Fouad Demami, Liang Ni, Gertrude Godem-Wenga IETR - Institut d’Electronique et de Télécommunications de Rennes FRANCE Rennes Rennes CMC2 - November 25, 2010 - Barcelona, Spain 2222 IETR - Institut d’Electronique et de Télécommunications de Rennes FRANCE MicroelectronicsMicroelectronics and and MicrosensorsMicrosensors DepartmentDepartment Two research teams involved Devices Development of process fabrication Microsensors Development of innovative sensors Development of process fabrication Development of innovative sensors Research fields covered : Competences and know - how Research fields covered : Micro/nano electronics Microtechnology/Microfluidic Competences and know - how Synthesis of Si related materials (thin films, nano-objects) Sensors Microsystems and systems Electronic on plastic substrates Si & Ge low temperature technology on flexible substrate Actuation and detection techniques C CMC2 - November 25, 2010 - Barcelona, Spain 3333 C hemical and biological detection Introduction ContextContext • Owing to their physical and electrical properties, silicon nanowires represent • a promising material with strong potential • large variety of applications in future nanoelectronic devices • Fabrication of innovative devices based on silicon nanowires with remarkable electronic properties. Ntiithlb • N ew t op i c i n th e l a b Our objectivesOur objectives • Synthesis of silicon nanowires • Study and optimization of their electrical performances • Fabrication of electronic devices (resistors, field-effect transistors) • Development of innovative micro sensors (chemical biological) CMC2 - November 25, 2010 - Barcelona, Spain 4444 • Development of innovative micro - sensors (chemical , biological) Silicon nanowires Benefits of silicon nanowires (SiNWs)Benefits of silicon nanowires (SiNWs) • High surface / volume ratio: surface phenomena predominate • Possibility of surface functionalization for biological applications • Development of nanosensors with high sensitivity Development of nanosensors with high sensitivity • Compatibility with CMOS technologies Silicon nanowires synthesis: 2 approaches Top - down Approach Bottom - up Approach Top down Approach Bottom up Approach Starts from bulk materials and scales down the p atterned areas Growth technique from molecular precursors using ti l tl t p nanopar ti c l es as ca t a l ys t s Optical and x-ray lithography E-beam and ion-beam lithography S i b lith h Layer-by-layer self assembly Molecular self assembly Di t bl CMC2 - November 25, 2010 - Barcelona, Spain 5555 S cann i ng pro b e lith ograp h y Printing and imprinting Di rec t assem bl y Coating and growth Outline Introduction • Context • Benefits of silicon nanowires (SiNWs) Sili i b tt h Sili con nanow i res: b o tt om-up approac h • Synthesis method • Fabrication of silicon nanowires based resistors El t i l h t i ti • El ec t r i ca l c h arac t er i za ti on • Chemical species detection Silicon nanowires: top down approach Silicon nanowires: top - down approach • Synthesis method • Fabrication of silicon nanowires based resistors • Fabrication of nanowires Thin Film Transistors ( SiNW TFT) • Fabrication of nanowires Thin Film Transistors ( SiNW - TFT) • Electrical characterization • Chemical species detection CMC2 - November 25, 2010 - Barcelona, Spain 6666 SiNW synthesis : Bottom-up • Nanowire synthesis is achieved by a vapor-liquid-solid (VLS) process Bottom-up approach Bottom-up approach A droplet of a liquid catalyst is put in contact with gaseous precursor molecules A droplet of a liquid catalyst is put in contact with gaseous precursor molecules . SiNWs are synthesized using gold (Au) as metal catalyst and silane (SiH 4 ) as precursor gas in a hot wall LPCVD reactor. CMC2 - November 25, 2010 - Barcelona, Spain 7777 SiNW synthesis : Bottom-up The diameter of the nanowire, grown by the VLS process, is given by the diameter of the gold nanoparticles. Nanowire Nanowire Au • Gold deposited by thermal evaporation (thickness below 5 nm), • Growth in LPCVD reactor with silane at 480°C (pressure: 40Pa) • Diameter : about 100 nm, various orientation, length can exceed 10 µm CMC2 - November 25, 2010 - Barcelona, Spain 8888 SiNW synthesis : Bottom-up Advantage of the VLS method : Advantage of the VLS method : • Possibility of selective doping (n- or p-type) of the nanowires, by controlled injection of the dopant precursor gas • High quality single crystalline nanowires with well-controlled composition and electronic properties Challenges: • Controlling diameter and orientation of the nanowires which impede the success of Controlling diameter and orientation of the nanowires which impede the success of the fabrication of nanowire arrays with high degree of reproducibility. CMC2 - November 25, 2010 - Barcelona, Spain 9999 SiNW synthesis : Bottom-up Highly in-situ doped polysilicon Fabrication of nanowires based resistors First mask Definition of the comb shape Electrodes geometry on a SiO 2 capped substrate SiO 2 polysilicon Silicon substrate Au Second mask Thin film Au local deposition after lift-of f technique nanowires nanowires Growth of SiNWs by LPCVD. Silicon nanowire network: used to interconnect electrodes CMC2 - November 25, 2010 - Barcelona, Spain 10101010 Silicon substrate or glass substrate (maximum process temperature 600°C) [...]... • Context • Benefits of silicon nanowires (SiNWs) Silicon nanowires: bottom-up approach Sili i b tt h • Synthesis method • Fabrication of silicon nanowires based resistors • El t i l characterization Electrical h t i ti • Chemical species detection Silicon nanowires: top down approach top-down • Synthesis method • Fabrication of silicon nanowires based resistors • Fabrication of nanowires Thin Film... require the use of high cost lithographic techniques) Compatible with conventional CMOS technology Benefits of excellent homogeneity and reproducibility of conformal CVD processes CMC2 - November 25, 2010 - Barcelona, Spain SiNW synthesis : Top-down Fabrication of silicon nanowires by the sidewall spacers formation technique RIE etching Polysilicon nanowires RIE etching Undoped polysilicon + Si poly... Barcelona, Spain SiNW synthesis : Top-down Top-down approach • starts from bulk materials and scales down the patterned areas • Advantages • high yield high uniformity and well aligned production of nanowires high-yield, high-uniformity, well-aligned • this approach is more promising for mass production of highly uniformed nanowire arrays and nanowire-based devices Sidewall spacer formation technique... November 25, 2010 - Barcelona, Spain 30 40 SiNW synthesis : Top-down To increase the surface… APCVD oxide Nanowire Nitride Sacrificial oxide process p 21 CMC2 - November 25, 2010 - Barcelona, Spain Conclusions and future directions Nanowires synthesis • Feasibility of silicon nanowires for both synthesis methods explored • Electrical behavior show good potential for electronic devices • Curvature radius... g e (V ) lt -8 -8 -2 ,0 x1 0 N+ Si-poly APCVD oxide 3 µm 5 µm 10 µm 20 µm -8 8 Current versus voltage o e gt s o s co a o es for 4 lengths of silicon nanowires Thermal oxide Silicon nanowires Si substrate 18 CMC2 - November 25, 2010 - Barcelona, Spain SiNW synthesis : Top-down Silicon Nanowire as gas sensor SiNWs device exposed to smoke 10 10 13 10 12 10 11 10 10 NH3 exposure 10 10 9 10 8 10 7 10 6... oxide Silicon oxide Monocristalline substrate 16 CMC2 - November 25, 2010 - Barcelona, Spain SiNW synthesis : Top-down Optmization of the steepness: dry etching parameters (pressure, power) + N Si poly Oxide Accurate control of the Si-poly etching : Nanowire oxide substrate Nanowires with curvature radius ~ 50 nm 17 CMC2 - November 25, 2010 - Barcelona, Spain SiNW synthesis : Top-down Fabrication of Nanowires. .. electrical behaviour Future directions • Detection of chemical and biological species (areas of healthcare, life sciences) • Nanowires: new opportunities in this interdisciplinary area sensed •  diameters comparable to those of the biological/chemical species being sensed • Devices based on nanowires: ultrasensitive electrical sensors for the detection of biological and chemical species • - ability to... donor of electrons  Carrier transport strongly depends on structural nanowires defects (polysilicon grain boundaries)  Gas molecules adsorbed may play a significant role in decreasing the potential barrier height at the grain boundaries between two grains 19 CMC2 - November 25, 2010 - Barcelona, Spain SiNW synthesis : Top-down Nanowires Field effect transistors using sidewall spacer process nanowires. .. Conclusions and future directions Detection of proteins Antibody receptor Nanowire modified with specific surface receptors  immobilization of antibodies  binding of antigens Binding of a protein Biological sensors • Specific sensing achieved by linking a recognition group to the surface of the nanowire • The nanowire surface can be modified with a variety of linker molecules (bioaffinitive agents):... (without using labels) • - low concentrations of DNA, proteins or viruses p y p • - rapid analysis of these species 22 CMC2 - November 25, 2010 - Barcelona, Spain Conclusions and future directions conductance time Detection of DNA-hybridization Probe binding P b bi di 23 P-type FET : the binding of target molecules (negative charges) leads to an accumulation of holes in the nanowire: conductance  No-complementary . (A) air 10 9 n ce () Reversible trend 2, 0x10 -8 4,0x10 -8 Curren t i 10 8 Resista n trend -25 0 0 25 0 500 750 1000 125 01500175 020 0 022 50 0,0 Time (sec) 21 min a i r 0 5 10 15 20 25 30 10 7 Time (min) NH 3 . (A) D G N + Substrate S 1E-7 0 123 4 -5,0x10 -9 0 , 0 Vds (volts) N Substrate 1E-9 1E-8 Ids (A) Vds = 4V 1E - 11 1E-10 CMC2 - November 25 , 20 10 - Barcelona, Spain 20 2 020 20 -10 0 10 20 30 40 1E 11 Vgs (volts) . d’Electronique et de Télécommunications de Rennes FRANCE Rennes Rennes CMC2 - November 25 , 20 10 - Barcelona, Spain 22 22 IETR - Institut d’Electronique et de Télécommunications de Rennes FRANCE MicroelectronicsMicroelectronics