Lateral Organic Field Effect Transistors (LOFET)

LOFET waferstack
LOFET waferstack

One further step in simplifying materials characterization is the analysis of basic logic circuits. Here, up to 36 single transistors are interconnected to inverters and ring oscillators. Monitoring of the active materials then only requires a frequency measurement of the ring oscillators which can be automated easily. This prevents the complicated and time-consuming measurement and analysis of the individual transistor characteristic. Furthermore, it is not only reliable information about logic capability that is acquired. The dynamic characteristics of the inverters are also determined.

Layout of the basic logic circuit with LOFET
Layout of the basic logic circuit with LOFET

The layout of a LOFET chip includes an initial block with eleven individual transistors making a complete para-meter extraction for circuit simulation possible. A second block contains four inverters which are replicated in the oscillators. These separately accessible inverter levels enable a detailed analysis of the transient behavior in case the amplification of the individual inverter stages is not sufficient for starting the oscillation of the ring oscillators. The third block contains ring oscillators with either seven or 15 stages. Each ring circuit has a three-stage output amplifier which decouples the oscillation inside the ring from the output terminal and allows a direct frequency measurement without external amplification.

The LOFET substrates are also produced in bottom gate architecture so that functional circuits require the deposition of the semiconductor layer only.