Analog Layout Topics Preview

Antenna effect:

       If long Metal interconnects is connected to the  poly gate if the charged particles stored in the metal during fabrication is sufficient to break thin gate oxide, which will act as a Antenna and it will breakdown the gate oxide beneath the poly gate.

Antenna Ratio =metal Area(am)/gate area(ag)

 

Preventions:

1)metal jumper:-
2)diode insrtion
3)dummy mos device.

Matching:

      To minimize the mismatch of the device parameters that is called matching
                              (or)
          To minimize  the PVT variation

Interdigitation;

         Here current will reflected to the near by device in which the gate terminals of all the device is shorted with drain and gate of source device.

Common centroid:

    It gives 100% gradients matching.

 

 

 

Gradients:

       Device should have same environment, same size, orientation,supply, temperature and location.

Latchup:

          It is a failure mechanism in which a low resistance path between vdd and gnd, due to turn on the parasitic BJTS.

 

 

 

Prevention's:

    Guard ring and Tap ring

Guard ring:

guard ring is need for protecting the noise to the devices from all sides like Diff pair and Current mirror.

current increases when Resistance Decreases.

Shielding:

      To avoid the cross coupling occurrence due to high frequency signals passing beside the critical signal.

1) side shielding
2)Coaxial shielding

           we need to shield low frequency net, if you shield high frequency net like clk is might add some cap which might slow it down.

ESD:

It is the sudden flow of static electric charge from one object to IC.

prevention:

All the input and output pins must have back to back esd diode connected to the Bond Pad.

Human body Model:

           mainly concentrates, when human touch the IC pins there would be sudden charge flow from human body to chip by using diodes to fix the human body event.

Charge Device Model:

            Chip will be between two parallel plates and charges, in this scenerio all layers in chip will get charges. this charge has to be discharge through any pin of the chip.
in this path there would be circuit whose gates connected to pad to protect these gate oxides we need to place CDM devices very close to gates.

Substrate noise:

      Current leakage due to Dynamic switching circuits.

      Using guard ring to avoid it.

STI:

It prevents leakage between two adjucent semiconductor devices is called sti.

 

 

 

LOD:

It is mainly occurs due to the shallow trench isolation(STI). while doing sti some mechanical force will applies on nearest diffusion. due to this Vt will varied.
to avoid LOD Effect can Add Dummy to the active devices.

Reduce the vt:

reducing the oxide thickness & by reducing the channel length. threshold voltage is reduced by incrasing the body and drain voltage we can also reduce Vt.

EM:

Gradual displacement of atoms in a conductor due to flow of electrons with high current densities.

Prevention's:

increase metal width
metal stack
by avoiding 90 degrees Bendings.

IR Drop:

Every metal have some resistance. due to the resistance of that metal voltage drop will occur, this is called Voltage or IR drop.

Preventions:

increase metal width
metal stack
using higher metal.

WPE:

During ion implantation, ions gets scattered at near photo resist edges and stored at well edges.
which makes more concentration at edges.

Using dummies at edges.

Vt:

minimum voltage required to create channel in mosfet.

Body effect :

source and bulk should be at same potential ,If we didnt connected to same potential threshold voltage will vary for particular device.

 

 

threshold voltage – Body effect:

• The change in the threshold voltage of a MOSFET, because of the voltage difference between body and source is called body effect

 

Cross talk:

Switching of the signal in one net can interfere neighbouring net due to crosscoupling capacitance it is known as crosss talk.

Preventions

Double spacing ,
multiple vias

Channel length modulation:

It can be define as he change or reduction in length of the channel(L) due to increase in the drain to source voltage in the saturation region.

 

Channel length modulation:

• The channel length of the MOSFET is changed due to the change in the drain to source voltage.
• This effect is called as the channel length modulation.

 

What is Via?

 It is used to connect higher level metals from metal1 connection. The design rule for contact is minimum 2x2 and same is applicable for a Via.

 

 

List of LVS errors. 

 

There are main two types of LVS errors. 

Extraction Errors 

• Floating text 

⚫ open text

 ⚫ short text 

  Extraction error 

• Stamping

 

 • Open- short LVS

 

 ⚫ Device mitch match error 

• Property errors

 • Port swap errors 

⚫ Unmatched nets in the layout/schematic

 • Unmatched devices in the layout/schematic

OHM'S LAW 

 

Ohm's law describes mathematically how voltage, current, and resistance in a circuit are related. Ohm's law can be written in three equivalents form, the formula you use depends on the quantity you need to determine. 

 

Ohm determined experimentally that if the voltage across a resistor is increased, the current through the resistor will increase; and, likewise, if the voltage is decreased, the current will decrease. Ohm also determined that if the voltage is held constant, less resistance results in more current, and more resistance results in less current. Ohm's law states that current is directly proportional to voltage and inversely proportional to resistance.

 

 I =V/R

 

 where I is current in amperes (A), V is voltage in volts (V), and R is resistance in ohms(Q).

 

 

 

What is a capacitor?

 

The capacitor is an electrical component used to store electric charge. The capacitor is made of two close conductors (usually plates) that are separated by a dielectric material. A capacitor has a properly to block d.c current and pass a.c. current. A passive component which has the ability to charge or store energy is called as capacitor

Semicondutor

semiconductors are materials which have a conductivity between conductors  and insulators.

semiconductors can be pure elements,such as silicon or germanium ,compounds such a gallium arsenide 

 

 

p-type

n-type

 

 

 

What Is a MOSFET?

Metal Oxide Silicon Field Effect Transistors commonly known as MOSFETs are electronic devices used to switch or amplify voltages in circuits. It is a voltage controlled device and is constructed by three terminals. The terminals of MOSFET are named as follows:

• Source
• Gate
• Drain
• Body

Depletion Mode

When there is no voltage across the gate terminal, the channel shows maximum conductance. When the voltage across the gate terminal is either positive or negative, then the channel conductivity decreases.

Enhancement Mode

When there is no voltage across the gate terminal, then the device does not conduct. When there is the maximum voltage across the gate terminal, then the device shows enhanced conductivity.

Operating Regions of MOSFET

A MOSFET is seen to exhibit three operating regions. Here, we will discuss those regions.

Cut-Off Region

The cut-off region is a region in which there will be no conduction and as a result, the MOSFET will be OFF. In this condition, MOSFET behaves like an open switch.

Ohmic Region

The ohmic region is a region where the current (I_DS)increases with an increase in the value of V_DS. When MOSFETs are made to operate in this region, they are used as amplifiers.

Saturation Region

In the saturation region, the MOSFETs have their I_DS constant in spite of an increase in V_DS and occurs once V_DS exceeds the value of pinch-off voltage V_P. Under this condition, the device will act like a closed switch through which a saturated value of I_DS flows. As a result, this operating region is chosen whenever MOSFETs are required to perform switching operations.

 

Why is MOSFET used?

What are MOSFETs used in? The MOSFET is the most common type of transistor today. Their primary use is to control conductivity, or how much electricity can flow, between its source and drain terminals based on the amount of voltage applied to its gate terminal.

 

 

 

What is a resistor?

Resistor is a passive two terminals electrical component used for regulating the flow of electricity in a circuit

 

 

 

sand to silicon

 

raw material sand primarily mad up of silicon dioxide

sand combined with carbon and heated to an extremely high  temperate and remove the oxygen

metallurgical grad silicon

98% pure silicon

we need to 100% pure silicon

Siemens process 

98% silicon and hydrochloride acid add with reactor and heated

99.9999% pure silicon

go for CZ ( Czochralski ) process 

take furnace and add 99.9999% silicon combined with p type or n type importunity's add to furnace

in furnace mixing with silicon negates and type of impurities(trivalent or pentavalent ), sheet rode dip in furnace or crusable if crusable is rotating clockwise means, sheet rode will rotate anticlockwise direction, then we get ingot.

that ingot slices by using diamond then we get wafer by the chemical mechanical process smoothing the surface of wafer