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Overview of drawing Resistor and Capacitor Layout in CMOS technology
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Resistors & Capacitors
Preethesh
ResistorsDummy resistor should be added in order to minimize the faster etching in large areas
Contact resistance must be taken into account for small resistance values
In order to minimize the noise, the resistor can be designed with a guard ring inside a well to reduce the coupling to the substrate
Matching between resistors requires that the resistors are designed in the layout :
with the same orientation distributed in a interdigitized or common centroid style
Resistor type Sheet resistance (/sq)
Polysilicon 100
n+ Diffusion 50
p+ Diffusion 100
n-Well 1000
Capacitors
A capacitor is made with two conductive layers (electrodes) insulated
by means of a dielectric layer.
Electrodes used : Metal, Polysilicon, Diffusion
Insulator : Silicon Dioxide, Polysilicon oxide, CVD oxide
Different kinds of capacitors are available in CMOS technology:
poly 1 to poly 2 (dielectric is thin silicon dioxide or other, e.g. thin sandwich of silicon dioxide, silicon nitride, silicon dioxide)
poly to implanted region (high-dose implantation under poly; dielectric is thin silicon dioxide);
poly to metal 1 (dielectric is intermediated CVD oxide); metal 1 to diffused active area (dielectric is intermediated
CVD oxide); metal 1 to metal 2 (dielectric is the intermetal insulator).
To achieve good matching : Use of unity capacitors connected in parallel Use W = L fairly large
MIM Cap
Metal-insulator-metal (MIM) structure situated in the oxide layers.
The insulator is a very thin layer (~25 nm), resulting in high density and relatively low back-plate parasitics.
MOM(Metal-Oxide-Metal ) Cap
Use lateral flux (~Lmin) and multiple metal layers to realize high capacitance values
• Matching limited by layer thickness variations
MOM capacitor, also known as VPP (vertical parallel plate) NVCAP (natural vertical capacitor) lateral flux capacitor comb capacitors interdigitated finger capacitor –
One of the most widely used, due to its good characteristics
Capacitor Types
Capacitor type Capacitance per unit area ( aF/m2)
MOM 150
MOS gate (biased) 5000
MIM (thin oxide option) 1000
Poly-poly 1000
Thank You ...