Electronic – the maximum allowable load capacitance for 74HC04

Yes, it is correct. I did not check the numbers, but the procedure is correct.

To help you understand what you are doing, here is an explanation of the formula. When you perform a read operation, you turn on the NMOS. This means that you somehow shortcircuit Cc and the bit line. These are two capacitors charged at different voltages, so when you connect them a redistribution of charges takes place. The formula that you are using is actually about charge conservation, and not energy conservation. The charge Q stored in a capacitor equals its capacity times the voltage across its leads: $$ Q\ =\ C \cdot V$$ So what you are doing is just match the charge present before the connection, and the charge present after, keeping in mind that after the short circuit we can model the Cc-BL capacitor as the parallel of the two. $$Q_i = Q_f \\ C_C\cdot V_{C_C}+C_{BL}\cdot V_{C_{BL}} = C_{tot}\cdot V_f$$ The final voltage must be greater than \$V_{C_{BL}}+\Delta V\$ if we had a high level and less than \$V_{C_{BL}}-\Delta V\$ if we had a low level. Using this condition will lead to two separate equations that are easily solved: $$ C_{C(1)} \ge \frac{C_{BL}\cdot \Delta V}{V_{C_C(1)}-V_{BL}- \Delta V} \\ C_{C(0)} \ge \frac{-C_{BL}\cdot \Delta V}{V_{C_C(0)}-V_{BL}+ \Delta V} $$

The higher value of capacitance is the one you are looking for.

The number of gates per unit area is a function of many parameters, including the particular design rules for each manufacturer. If one manufacturer has more layers of interconnect than another then the effective gate density may be much higher even if the transistor geometry is very similar. The architecture and structure of the chip can also be a factor. For example, chips where a large fraction of the area is devoted to memory will have more transistors per unit area than chips that have complex processors. Manufacturers often assume that four transistors is the equivalent of a gate, which is a pretty crude metric. The bottom line is that comparing different IC manufacturers at a given process node, or the same manufacturer at different process nodes, is not very meaningful.