Fabrication of Passive Elements(Resistor ,Capacitors & Inductors)
• Integrated Circuit• Resistors• Capacitors• Inductors• Uncertainty in IC FabricationContent
Integrated CircuitAn integrated circuit (IC) is a miniature ,low cost electronic circuitconsisting of active and passive components fabricated together ona single crystal of silicon. The active components are transistorsand diodes and passive components are resistors, inductors andcapacitors.
Advantages of Integrated Circuit1. Miniaturization and hence increased equipmentdensity.2. Cost reduction due to batch processing.3. Increased system reliability due to the eliminationof soldered joints.4. Improved functional performance.5. Matched devices.6. Increased operating speeds.7. Reduction in power consumption
IntroductionA resistor is a passive two-terminal electrical component that implementselectrical resistance as a circuit element.The current through a resistor is in direct proportion to the voltage across theresistors terminals. This relationship is represented by Ohm’s law (I=V/R)I is the current through the conductor in units of amperes, V is the potentialdifference measured across the conductor in units of volts, and R is the resistanceof the conductor in units of ohms.
Resistance of MaterialOther conducting materials OhmN+ polysilicon (t=500 nm) 20Aluminum 0.07Silicided Polysilicom 5Silicided Source/drain diffusion 3MOSIS 1 um CMOS PROCESS
IC ResistorGiven the sheet resistance, we need to find the number of squares for this layoutL / W = 9 squares
Laying Out a ResistorRough approach:R known(Ns) = R / Rs(Sheet Resistance)Select a width W (possibly the minimum to save area)the length L = W N and make a rectangle L x W in areaAdd contact regions at the ends ... ignore their contribution to R
Layout of ResistorMore careful approach:Account for the contact regions and also, for cornersMeasurement shows that the effective number of squares of the “dogbone” stylecontact region is 0.65 and for a angle 90 corner is 0.56.For the resistor with L / W = 9, the contact regions add a significant amount tothe total square count:Ns= 9 + 2 (0.65) = 10.3
IntroductionCapacitor is a basic storage device to store electrical charges andrelease it as it is required by the circuit. In a simple form it is made oftwo conductive plates (Electrodes) and an insulating media(Dielectrics) which separate the electrodes.The charges (Q) on the capacitor plates depend on the voltage (V)andthe capacitance value (C) and is as follows:Q=C.V
FabricationB+n-SiSiO2n-SiGROW 4000 A OXIDE ON N-TYPE SILICON MATERIAL PATTERN AND ETCH OXIDE<THEN ION IMPLANT 50 KeVBORON TO FROM P+ REGION
Thin SiO2Aln-Si n-SiGROW THIN OXIDE (2000 A) PATTERN ANDETCH OXIDE TO FROM CONTACTDEPOSIT 5000A ALUMINUM PATTERN ANDETCH ALUMINUMFabrication
Metal-Metal CapacitorsThis type of structure is easily built in multiple-metal layer processes. The capacitors are formed usingpatterns on two metal layer.Cmm = Cxy *AovWhere Cxy is the capacitance per unit area andAov is overlap area.
MOSFET CapacitorsThe gate implementation of capacitance of MOSFET also can be used to create a capacitor by shorting boththe drain and source connectionsC=Eox/tox*Ag=CoxWL
Introduction An inductor (also choke, coil or reactor) is a passive twoterminal electrical component that stores energy in its magneticfield. For comparison, a capacitor stores energy in an electricfield, and a resistor does not store energy but rather dissipatesenergy as heat. Any conductor has inductance. An inductor is typically made ofa wire or other conductor wound into a coil, to increase themagnetic field.
Construction of an inductorAn inductor is usually constructed as a coil of conductingmaterial, typically copper wire, wrapped around a core either ofair or of ferromagnetic or ferrimagnetic material. Core materialswith a higher permeability than that of air increase the magneticfield and confine it closely to the inductor, thereby increasing theinductance.
Silicon wafer Deposit 100nm of SiO2Fabrication
Spin coat photo resist Mask exposure and develop the patternFabrication
Deposit aluminum and copper alternately Photo resist removal.Fabrication
Schematic layer StructureMicrophotograph of the spiral inductor fabricated on the A1203 substrateSchematic layer structure of the spiral inductor fabricated on the A1203 substrate
The precision of transistors and passive components fabricated using ICtechnology is surprisingly, poor!Sources of variations: Ion impant dose varies from point to point over the wafer and from wafer towafer.Thicknesses of layers after annealing vary due to temperature variations acrossthe wafer.Widths of regions vary systematically due to imperfect wafer flatness (leading tofocus problems) and randomly due to raggedness in the photoresist edges afterdevelopment.Uncertainties in IC Fabrication