Assertion (A) : The value of thin film resistor can be changed even after fabrication. Reason (R) : This is done by means of trimming. Select your answer using the codes given below.
Both (A) and (R) are true and (R) is correct explanation of (A).
Examine the assertion. A thin-film resistor is a strip of resistive material — nichrome, tantalum nitride or cermet — deposited a few hundred nanometres thick on a substrate. Its value is
\(R=R_s\dfrac{L}{W}\)
where Rs is the sheet resistance in ohms per square and L/W is the number of squares. Because the film is exposed on the surface, its geometry can still be altered after the wafer is made. The assertion is true.
Examine the reason. The process for doing this is called trimming. Material is removed from the film — classically by abrasive or laser cutting — which narrows the effective width or lengthens the current path, so the resistance can only be adjusted upward, and only in the increasing direction. The reason is true.
Does the reason explain the assertion? Yes, completely and directly. The assertion states that the value can be changed after fabrication; the reason names the exact mechanism by which that is done. There is nothing else to the claim — trimming is the answer to "how". So (R) is the correct explanation of (A), which is code 1.
How trimming is actually carried out.
| Method | Action |
|---|---|
| Laser trimming | A focused laser vaporises an L-shaped or plunge cut into the film; resistance is monitored live and the beam stops at the target value. |
| Abrasive trimming | A fine air-driven abrasive jet erodes the film — cheaper, coarser. |
| Anodisation | Electrochemical oxidation of a tantalum film thins the conducting layer. |
Because the value is measured in a feedback loop while the cut proceeds, tolerances of 0.01 % are achievable — far better than the ±10 % typical of an untrimmed deposited film, and far better than any diffused resistor can offer.
The contrast with monolithic resistors. A diffused resistor is buried under an oxide layer, so its value is fixed the moment the diffusion is done and cannot be altered. This ability to trim is a principal reason thin-film networks are chosen for precision analogue work such as data converters and instrumentation amplifiers, where matched, accurate ratios matter.
Hence, both statements are true and (R) is the correct explanation of (A).
Similar Questions
Given below are two statements :
Statement I : Concentration of acceptor atoms in the region between isolation islands in a monolythic integrated circuit will be much higher then in a p-type substrate.
Statement II : The higher density is provided to prevent the depletion region of the reverse biased isolation to substrate junction from extending into the p+ type material.
In the light of the above statements, choose the most appropriate answer from the options given below :
Arrange the following fabrication steps in order needed to fabricate the IC :
(a) Oxidation (b) Etching (c) Metallization (d) Epitaxial growth
Codes :
Assertion (A) : In a bipolar IC fabrication, the diode isolation is used to isolate one device from the other.
Reason (R) : P+n diode used as isolation diode in IC fabrication.
Select your answer using the codes given below.
Assertion (A) : The epitaxial layer growth possesses the same crystal structure to that of the substrate on which it is grown.
Reason (R) : It can only be of similar conductivity type but possesses different value of resistivity to that of the substrate.
Select your answer using the codes given below.
In an npn diffused junction transistor, the p-type base region is formed on the n-type collector region through the process of :
The evaporation rate from a clean surface is related to the equilibrium vapour pressure Pe of the evaporating species of molecular weight M by an expression :
Czochralski (Cz) method is used instead of using float zone technique to grow Si crystal because it produces :
Czochralski system of crystal growth is a
MEMS devices are within the size range of
The thermal oxidation of silicon single crystal producer stacking faults lying on the plane.
Important Questions from Device Technology
Given below are two statements :
Statement I : Concentration of acceptor atoms in the region between isolation islands in a monolythic integrated circuit will be much higher then in a p-type substrate.
Statement II : The higher density is provided to prevent the depletion region of the reverse biased isolation to substrate junction from extending into the p+ type material.
In the light of the above statements, choose the most appropriate answer from the options given below :
Arrange the following fabrication steps in order needed to fabricate the IC :
(a) Oxidation (b) Etching (c) Metallization (d) Epitaxial growth
Codes :
Assertion (A) : In a bipolar IC fabrication, the diode isolation is used to isolate one device from the other.
Reason (R) : P+n diode used as isolation diode in IC fabrication.
Select your answer using the codes given below.
Assertion (A) : The epitaxial layer growth possesses the same crystal structure to that of the substrate on which it is grown.
Reason (R) : It can only be of similar conductivity type but possesses different value of resistivity to that of the substrate.
Select your answer using the codes given below.
In an npn diffused junction transistor, the p-type base region is formed on the n-type collector region through the process of :
