MSE1110_HW2Solutions - MSE1110/ENGRI1110 Homework #2...

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MSE1110/ENGRI1110 Homework #2 Solutions 1. (15) The time to turn on a MOSFET is directly proportional to the product of the gate resistance and the capacitance of the gate. The gate resistance is proportional to the area of the gate times the thickness of the metal used for the gate. The capacitance of the gate is proportional to the area of the gate divided by the thickness of the gate oxide. If the length and width of the gate, the thickness of the gate metallization, and the thickness of the gate oxide are all multiplied by the same factor n, where n< 1, then how does the time to turn on the MOSFET scale? (Use mathematical equations for your answer). Translating the problem statement directly into mathematics, the first three sentences yield: oxide metal T A C AT R RC τ Substituting the resistance, R, and the capacitance, C into the equation for the time, , to turn on the MOSFET, we find: τ oxide metal T T A 2 We know area is length by width, thus: oxide metal T T lw 2 ) ( We then multiply the specified components in the equation by a factor, n. oxide metal oxide metal T T lw n nT nT lw n 2 4 2 2 ) ( ) ( = Bringing the multiplication factor out front, we see that the time to turn on the transistor scales with n 4 . Such factors inspire the drive for smaller transistors. 2. (10) The color emitted from an LED is roughly its band-gap energy.
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What composition, if any, of GaP x A 1-x (see Figure below) would you use to make an LED that emits red (1.7 eV), yellow (2.1 eV) or green (2.3 eV). Can a blue (2.8 eV) LED be made from this family of solids? Why or why not? a) x = 0.25 for red (GaP 0.25 As 0.75 OR Ga 4 PAs 3 ), x = 0.75 for yellow (GaP 0.75 As 0.25 OR Ga 3 P 4 As) , and x= 1.0 for green (GaP) b) A blue LED cannot be made with a band gap of 2.8 eV because given this family of solids, the unit cell cannot be made small enough. There is an inverse relationship between
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This note was uploaded on 10/25/2009 for the course ENGRI 1110 at Cornell University (Engineering School).

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MSE1110_HW2Solutions - MSE1110/ENGRI1110 Homework #2...

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