Resistance Flashcards
What are two applications of resistors?
- Current limiting (regulate amount of current)
2. Voltage division
What is Ohm’s Law?
V = IR, or R = V/I or I = V/R
How to calculate resistance of resistors in series?
Rab = R1 + R2 + R3
How to calculate resistance of resistors in parallel?
1/Rab = 1/R1 + 1/R2 + 1/R3
- What are three names for what ρs stands for?
1. What is the standard unit for ρs?
- Sheet rho, sheet resistivity, sheet resistance.
1. Ohms per square.
What are Kirchoff’s Laws?
Kirchoff’s Voltage Law = Vt = V1 + V2 + V3 + …
Kirchoff’s Current Law = It = I1 + I2 + I3 + …
What is the basic sheet resistivity equation?
Rab = ρs * (L / W) Ω
What are the two main types of fabricated resistors?
- Deposited resistors such as poly or thin-film resistors.
2. Implanted resistors such as N+, P+, N- (nwell) and P- (pwell) resistors.
What is a “device recognition layer”?
What are common names for resistor and capacitor device recognition layers?
- A layer commonly added on layouts to help programs such as LVS and DRC to recognize certain devices.
- rmask or rdef (resistor definition layer), cmask or cdef
What is a thin-film resistor commonly made out of?
What is the typical range of sheet rho?
What is an advantage?
What is a disadvantage?
- nickel- or silicon-chromium.
- a few to several thousand ohms per square.
- On same level as a metal, so no contacts needed.
- Additional costly specific process steps.
What are two ways to increase the accuracy of a resistor when using the basic resistor equation?
- Avoid using narrow diffusions, to avoid large out-diffusion effect.
- Use more terminal contacts to reduce ohmic contact resistance.
What are two issues that complicate the basic resistance equation?
- The out-diffusion effect or “etching effect” (diffusion tends to be wider than drawn)
- The ohmic contact resistance (the contacts have some resistance as well).
What is the more advanced resistance equation?
Rab = (ρs * (L / W+2ΔW)) + 2Rcontact Ω
What equation describes the switching speed of a logic? AKA propagation delay?
Fs = 1 / 2RC Fs = Switching frequency (per second?) Propagation delay R = Load resistance C = Load capacitance delta t = RC (RC time constant)
Name five ways to reduce parasitic resistance
- Use good conductors to form connections, especially for long and heavily-loaded lines. Higher layer metals are preferred because they are thicker (reduced sheet rho) and less capacitance with surrounding layers.
- Shorting bar technique, strap poly with metal.
- More contacts and vias
- Minimum spacing between diffusion contacts and active gate area.
- Fabricate low resistance polys (silicidation).
- What metals are typically used for silicidation?
2. What are the resulting polys or diffusions called?
- Tungsten, titanium, molybdenum
2. Silicided or clad polys, clad diffusions or moats
What are two common names for the method of ignoring silicide to create resistors?
- Silicide-Block Layer
2. RPO (Resist Protection Oxide) in TSMC design rules
What does Ids stand for?
Current from source to drain.
What are the terms for running metal over, or running diffusion under?
“jumper” and “tunnel”
What is the name for a “fingered” resistor?
“Segmented” resistor.
What the name for moving a chip to a new technology?
What are easier to migrate, resistors or capacitors, and why?
- “Technology migration”.
2. Resistors, because the resistance equation is based on ratios that don’t change when you scale them.
What is an advantage of implanted resistors over deposited resistors?
They disperse heat better.
What is a case when you will create long diffusions?
Guard rings
What does RPO stand for?
Resist Protection Oxide (for creating non-silicided materials)
