738
24 Transistors
(a)
(b)
Fig. 24.54 a Optical image of transparent MESFET inverter based on ZnO. The two rectangles indicate the two gates.
b Transfer characteristic for supply voltage V DD =4 V
10
6 . Also, a thinner channel allows further gate size scaling. However, the realities are complicated
[2143, 2144] and clear performance gains have not been achieved yet. Also, the upscaling to wafer
size is an unresolved issue.
24.6.4 OFETs
Organic field effect transistors (OFETs) [2139, 2145–2147] are transistors for which at least the channel
consists of an organic material. Most work is done on thin film transistors, although some work on
OFETs using bulk organic semiconductors has been reported [2148, 2149]. Organic materials are
also used for the insulator and the contact materials. Often organic and flexible substrates are used.
Applications are in low cost electronics, e.g. for driving display pixels or RFID tags (typically operating
at 13.56 MHz or 900 MHz). Processes like spin-on and printing can be used. Due to their larger chemical
stability against oxidation, mostly p-type channel materials are used. The highest mobilities are reached
for pentacene (6 cm
2 /Vs) and sexithiophene (1 cm
2 /Vs); n-type organic semiconductors exhibit field
mobility below 0.1 cm
2 /Vs [2145].
24 Transistors
(a)
(b)
Fig. 24.54 a Optical image of transparent MESFET inverter based on ZnO. The two rectangles indicate the two gates.
b Transfer characteristic for supply voltage V DD =4 V
10
6 . Also, a thinner channel allows further gate size scaling. However, the realities are complicated
[2143, 2144] and clear performance gains have not been achieved yet. Also, the upscaling to wafer
size is an unresolved issue.
24.6.4 OFETs
Organic field effect transistors (OFETs) [2139, 2145–2147] are transistors for which at least the channel
consists of an organic material. Most work is done on thin film transistors, although some work on
OFETs using bulk organic semiconductors has been reported [2148, 2149]. Organic materials are
also used for the insulator and the contact materials. Often organic and flexible substrates are used.
Applications are in low cost electronics, e.g. for driving display pixels or RFID tags (typically operating
at 13.56 MHz or 900 MHz). Processes like spin-on and printing can be used. Due to their larger chemical
stability against oxidation, mostly p-type channel materials are used. The highest mobilities are reached
for pentacene (6 cm
2 /Vs) and sexithiophene (1 cm
2 /Vs); n-type organic semiconductors exhibit field
mobility below 0.1 cm
2 /Vs [2145].