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 ...