Week 1

This week is the first week of the project session, we discussed the whole project and decided each group member's role. In addition, we learned basic knowledge of organic CMOS inverters that would be useful for our project. 

Structure:
Complementary metal oxide semiconductor (CMOS) is an ingenious circuit which is built from a pair of NMOS and PMOS transistors operating as complementary switches (Fig 1). The PMOS is connected between VDD and the output node, while the NMOS is connected between the output node and the ground. CMOS has a symmetrical structure which means each device has an equal and opposite effect.

Fig 1

Operate Principles:
When input voltage is small, the NMOS transistor is switched off, while the PMOS is switched on. When input voltage is large, the PMOS is switched off.

Voltage Transfer Characteristic(VTC):
The output curve (Fig 3) of a CMOS inverter can derived from the superposition of the output curves (Fig 2) of NMOS and PMOS.

Fig 2

Fig 3

In region 1, when 0≤Vin<Vtn the NMOS is cut off, the PMOS switch is closed.
In region 2, when Vtn<Vin<VDD-|VTp|, both NMOS and PMOS are switeched on and there is a current flowing between VDD and GND which means there is power dissipation in the type of heat.
In region 3, when Vin>VDD-|VTp|, the PMOS is cutt off and NMOS switch is closed.

The advantage:
CMOS is built out of transistors operating as switchers without any other passive elements like resistors and capacitors, as a result, it is much power efficient.
It can also be derived from the fact that in region 1 and 3, there are no current between VDD and GND, in other words, there is no power dissipation in region 1 and 3.

The organic CMOS and PMOS will be analysed under different conditions during the project. Moreover, an organic semiconductor would be used in the channel of the organic field-effect transistor (OFET). For the further search on organic semiconductor, we found some useful articles for deeply understanding. Basic characterization of organic semiconductor are shown in the following link:

http://www.sciencedirect.com/science/article/pii/S004060909900944X

Next week, we are going to apply MATLAB to do the simulation in order to find the voltage transfer characteristic curves of CMOS and PMOS inverters.