4.1 High temperature heating elements and electrodes Metal Heating element 1. High melting temperature 2. Chemically inert 3. Good adhesion to substrate materials 4. Low cost Ex) Pt, Mo, W, Rh, Ru P =IV=I 2 R = V 2 /R Ceramic Heating element 1. High melting temperature 2. Chemically inert 3. Low cost - Typical resistivities: 0.01 1 Ω cm - Typical dimension of rod : 1m long and 0.5-2 cm in diameter Ex) SiC, MoSi 2, LaCrO 3 R operation voltage difficult to avoid current leakage Difficult in furnace design 4.1 High temperature heating elements and electrodes P =IV=I 2 R = V 2 /R R operation voltage difficult to avoid current leakage Difficult in furnace design In reducing atmosphere -graphite, Mo, and W can be used In oxidizing atmosphere - Pt can be used up to 1500 o C
4.1.1 Silicon Carbide - Protective oxide layer Hard materials - Stable in air up to 1650 o C - used as abrasive, refractory, and heating element - Hardness (~ 9 in Mohs scale) particularly at high temp. - Electrical conductivity - High thermal conductivity - Low thermal expansion coefficient - Good thermal shock resistance Good materials for high temperature heating element. Fabrication of SiC 1) Acheson process (1891) - Heating a mixture of finely divided carbon and silicon at ~1000 o C 2) Current fabrication procedure - Passing a large electric current through a mixture of sand and coke - temperature up to ~2500 o C 4.1.1 Silicon Carbide Fabrication of SiC heating element 1. in situ formation of SiC from carbon and SiO 2. Reaction-bonding of SiC 3. Pressureless-sintering
4.1.1 Silicon Carbide Spiral type http://www.sojae.com/ 4.1.2 Molybdenum disilicide 4.1.3. Lanthanum chromite MoSi 2 - Heating element at > 1500 o C - ρ(r.t.) = 2.5X10-6 Ω cm - ρ(1800 o C) = 4X10-6 Ω cm - Known as Kanthal Super - MoSi2 particles bonded wit an aluminosilicate glass phase (~20% of the total V) LaCrO 3 - Heating element at > 1500 o C - ρ(r.t.) = 2.5X10-6 Ω cm - ρ(1800 o C) = 4X10-6 Ω cm - Known as Kanthal Super - MoSi2 particles bonded wit an aluminosilicate glass phase (~20% of the total V)
4.1.4 SnO 2 Applications - High temperature conductor - Ohmic resistor - Transparent thin film electrode - Gas sensor - Rutile structure - Mineral name cassiterite - Pure SnO 2 is good insulator -ρ(r.t.) = 2.5X10-6 Ω cm [Vo ] 0.1eV CB E g =3.7 ev 2SnO2 VB - oxygen deficient or antimony doped-sno 2 is n-type semiconductor 1 SnO OO O2 ( g) + VO + 2e 2 x 2 1 2 5 Sn O 2 Sb O 2Sb + 4 O + O ( g) + 2 e' 2 r 6 (Sn 4+ )=0.69Å r 6 (Sb 5+ )=0.61Å Similar size 4.1.4 SnO 2 (sintering) - Hard to sinter due to its evaporative decomposition at >1100 o C 1 SnO2( s) SnO( g) + O2( g) 2 In order to promote sintering of SnO 2 Sintering additive -ZnO: r 6 (Zn 2+ )=0.75Å -CuO: r 6 (Cu 2+ )=0.73Å Sintering in oxidizing atmosphere to reduce the evaporation Temp. 1 SnO2( s) SnO( g) + O2( g) 2 Oxidizing atmosphere Cooling in reducing atmosphere to increase n-type semiconductivity due to oxygen deficiency σ(r.t.) = 10 3 /cm 1 OO O2 ( g) + VO + 2e 2 reducing atmosphere time
4.1.4 SnO 2 (Electrode for Glass Melting) Refractory Furnace Structure Tin oxide electrode I 2 R glass Preheating of cullet using gas or oil to ~1000 o C SnO 2 electrode have enough σ for Joule heating (I 2 R) Heating from within the body of glass melt using SnO 2 electrode Lowers the surface temperature of glass melt Excessive loss of volatile element such as PbO can be avoided Strong against chemical attack can be used for 2 years Transparent electrode The driver should watch outside carefully. To see clearly, the frost in the window should be removed. Transparent electrode can be considered as on possible solution to remove the frost.
4.2 Ohmic resistor Resistor for electrical and electronic applications - Ohmic behavior - small dependence of R value upon T - R range : 10 3 ~ 10 8 (Ω) Suppose the situation that we should the resistance (10 5 Ω) in the length of 110 mm (0.11 m) with the materials (10-6 Ω m) 5 l 6 0.11m 6 0.11m 12 10 Ω= R= ρ = 10 Ωim A 10 = Ω im = 1.1X10 m 5 A A 10 Ω 1 µm X 1 µm X 110 mm possible to fabricate Another approach 4.2 Ohmic resistor Approaches to achieve high resistance in a small volume 1. Deposition of very thin conductive layers on insulating substrate l R = ρ A 2. Composite between conductive and insulating materials insulating conductive
4.2 Ohmic resistor : 4.2.1 Thin films Very thin film with the thinness of 10 nm can be realized by 1) Evaporation 2) Sputtering 3) Chemical Vapor Deposition Metal evaporation Oxide Sputtering ITO (90In 2 O 3-10SnO 2 ) Transparent conductive films Important in many electro-optical devices Application of ITO: 1. Electrochromic glass An electrochromic car roof maximizes the light and comfort inside vehicles in summer and in winter, whatever the sunlight factor, by modulating the transmission of light. The electrochromic roof is made of laminated glass which also gives it a shatter-proof quality. The inner surface of one of the glass sheets is multi-coated with an electrochromic film, around one micron thick. The stacked electrochromic layers act like a battery, the electrodes and electrolyte of which constitute thin layers of transparent minerals whose color changes with the charge. The application of a voltage colors the glass. The glass only needs to be short-circuited or a reverse polarity voltage applied to render it colorless. In the absence of any voltage, the glass has a memory effect and retains its previous coloration. This means that the glass draws current only during the coloring and clearing phases. http://www.saint-gobain-recherche.com/anglais/telectr.htm http://www.avatec.co.kr/product11.html
Application of ITO: 2. Touch Screen in LCD display 1. Polyester Film 2. Upper Resistive Circuit Layer 3. Conductive ITO (Transparent Metal Coating) http://www.visiontouch.com/5_ts/ts_tech/tec.htm 4. Lower Resistive Circuit Layer 5. Insulating Dots 6. Glass/Acrylic Substrate 7. Touching the overlay surface causes the (2) Upper Resistive Circuit Layer to contact the (4) Lower Resistive Circuit Layer, producing a circuit switch from the activated area. 8. The touchscreen controller gets the alternating voltages between the (7) two circuit layers and converts them into the digital X and Y coordinates of the activated area. http://www.touch-screens.com/touchscreens/resistive-touchscreens.html Application of ITO: 2. Touch Screen in LCD display
Application of ITO: 3. Electroluminescent Lamp ITO sputtered polyester (ITO: lamp s outer electrode) Bus Bar (Ag, to achieve maximum current to the coating Phosphor (light emitting layer) Barium titanate (dielectric insulator) Rear electrode (Ag or conductive carbon ink) Application of ITO: 3. Electroluminescent Lamp Characteristics of EL Principle: the rapid charge and discharge of phosphor by applying AC current result in the emission of light - Flexible and thin - minimal heat(cold light source) C - small power consumption (including the inverter efficiency) (AC 100 ~ 220 V usually used) (In the case of DC battery system, the inverter is required) - easy to replace - easy to fabricate the large-area display - weak to moisture (applications) - back-lightning LCD displays - control panel - advertising display D C D
Application of ITO: 3. Electroluminescent Lamp Fig. The phosphors used in EL lamps will emit either green, blue, or yellow light. White light can also be generated by mixing phosphors or adding dyes Fig.: Selective printing of EL lamp areas Printing all components of EL lamps is especially useful when the switch design calls for small-area lighting of individual keys. By printing a separate lamp area for each key, you'll minimize ink consumption and keep the lamp from drawing excessive power. Lighting watch faces Flexible lamp http://www.screenweb.com/industrial/cont/el_lamps990128.html 4.2.2 Thick film stress Utilize shear thinning at the high stress during the screen printing process - the shear rate(viscosity) decreases after screen printing F A = η Pseudoplastic dv dy Shear rate Velocity gradient From P.J.Holmes and R.G.Loasby, Handbook of thick film technology,
4.2.2 Thick film From P.J.Holmes and R.G.Loasby, Handbook of thick film technology, 4.2.2 Thick film Composition of Ink vehicle 1. Binder : viscosity control 2. Surface active agent : dispersion of the solid particles and adequate wetting of the substrate 3. Flow control agent : restrict ink flow during drying (ex.) Butyl carbitol acetate (Solvent) 69.12% Ethyl cellulose (Resin) 14.4% 2-Furoic acid (Flow control agent) 6.4% Nonyl phenoxypolyoxyethylene ethanol (Surfactant) 10%
4.2.2 Thick film Calendaring to disperse the components conductive powder powdered glaze organic vehicle Temp. ( o C) evaporation of organic solvent Binder burnout bonding of glass and resistive component to substrate via heat treatment time 4.2.2 Thick film active component: highly conductive oxides (10 5 10 6 S/m) PdO, RuO 2, Bi 2 Ru 2 O 7 and Bi 2 Ir 2 O 7 Typical glaze composition: 52PbO-35SiO 2-10B 2 O 3-3Al 2 O 3 glass High ρ NTC Low ρ PTC Dispersion of metal in an insulating matrix: abrupt change in ρ (percolation) ρ 5-6 orders Thick film resistor: gradual change in ρ 10 vol% ρ NTC PTC
Applications : Chip resistor http://www.western-resistor.com/ and http://www.resistor.com Applications : Chip resistor Resistor Requirements 1. Wide resistivity range 2. Low TCR 3. High stability to - Temperature variation - Voltage variation - Mechanical stress - Atmospheric variation - Laser trimming 4. Compatible with conductor termination 5. Low process sensitivity
Applications : Chip resistor Plunge cut L - cut Double L - cut Double plunge cut Serpentine cut L - cut with vernier Wider resistor (smaller R value : about 70-80%) than expectation for subsequent trimming Trimmable Chip Resistor : Trimming by user Applications : Chip resistor 적층세라믹칩콘덴서 (MLCC) 에이어칩저항기도가로세로 0.6 0.3 mm크기의이른바 0603 시대가막이올랐다. 삼성전기 ( 대표강호문 http://www.sem.samsung.co.kr) 는기존칩저항기의최소형제품인 1005(1.0 0.5 mm ) 보다부피가 60% 줄어든 0603 칩저항기를자체개발, 오는 8 월부터양산에들어갈계획이라고 11 일밝혔다. 삼성전기가개발한 0603 칩저항기는기존 1005 제품에비해부피가 60% 나줄어들었으나공급단가가 10 배이상비싼고부가가치제품이다. 이회사는오는 8 월부터양산체계를갖춰월 2000 만개가량생산, 내년한해동안 2 억개를판매한다는계획이다. 칩저항기는전자회로내에서전류와전압의세기를조절하는범용핵심부품으로노트북 (350 개 ) 이동전화 (100 개 ) PDA(200 여개 ) 등에대당수백개씩사용되고있으며세계시장규모는연간 14 억달러대다. 삼성전기는이번 0603 칩저항기개발로기존 0603 MLCC 와 0603 칩저항기등고부가가치제품의매출비중을올해 50% 까지확대, 초소형칩부품시장을선점한다는계획이다. 이회사는이미지난해말세계최소형인 0603 크기의 MLCC 를개발, 양산중이다. 삼성전기는이를계기로지난해말세라믹재질의 0603 칩인덕터 ( 용량 22nH) 를개발, 올하반기부터본격적으로양산하고내년에는 0402(0.4 0.2 mm ) 칩저항기도개발할계획이다. 이회사김정일과장은 0603 칩저항기는경박단소화라는장점이외에휴대형장비에있어가장중요한배터리의사용시간을좌우하는전력소비량을최소화시킬수있는장점을갖는다는점에서의미가크다 고말했다. MLCC 에이어이번에칩저항기의 0603 시대가열림에따라각종전자 정보통신기기에사용되는칩부품의 0603 시대가더욱본격화될것으로전망된다. 특히전자제품의경박단소화와초소형휴대기기의등장으로이제까지국내칩부품시장을주도해온 1005 칩부품은부품의실장공간을획기적으로줄일수있는 0603 칩부품으로급속히대체될것으로전망된다. < 안수민기자 smahn@etnews.co.kr> 전자신문 2002 년 4 월 12 일자