A RAM (random access memory) integrated chip contains transistors, in which there are doped semiconductors, and capacitors - Leaving Cert Physics - Question b - 2019

Doping a semiconductor involves adding an impurity to change its electrical properties. This procedure modifies the number of charge carriers available in the semiconductor material.

To create a n-type semiconductor with electrons as majority charge carriers, an element with more valence electrons than silicon (which has four) is added. For example, phosphorus, which has five valence electrons, donates one electron, thereby increasing the number of free electrons.

To make a p-type semiconductor with holes as majority charge carriers, an element with fewer valence electrons than silicon is introduced. For instance, adding boron, which has three valence electrons, creates 'holes' or vacancies in the semiconductor, enhancing hole concentration.

The energy stored, E, in a capacitor can be calculated using the formula: $E = \frac{1}{2} CV^2$ Substituting the values:

• Capacitance, C = 90 ff = 90 \times 10^{-15} F
• Voltage, V = 1.2 V

Thus, $E = \frac{1}{2} \times (90 \times 10^{-15}) \times (1.2)^2$

Calculating gives: $E = 6.48 \times 10^{-14} J$

Using the formula for charge, Q: $Q = CV$ Substituting in our values: $Q = (90 \times 10^{-15}) \times (1.2)$

We find: $Q = 1.08 \times 10^{-13} C$

To find the number of additional electrons, we divide the total charge by the charge of a single electron ($e = 1.6 \times 10^{-19} C): $number\ of\ additional\ electrons = \frac{1.08 \times 10^{-13}}{1.6 \times 10^{-19}} = 675000$