Organic Field Effect Transistors (OFET)

OFET waferstack
OFET waferstack

If an organic semiconductor layer is deposited on such a substrate, the Si-bulk acts as gate electrode and controls the channel current between the gold electrodes on top. A suitably doped Si-SiO2 interface in CMOS quality guarantees a reproducible gate contact. Gold electrodes with a patented undercoating suppress the formation of injector barriers between the gold electrodes and the organics in the transistor channel. This guarantees reliable ohmic source / drain contacts in the OFET even for p-type semiconductors. Due to both reliability and reproducible preparation, these substrates are applied for standardized material screening by all key developers of organic semiconductors all over the world.

OFET chip layout
OFET chip layout

In the standard OFET layout, each 150 mm wafer has 960 individual transistors on 60 chips, each sized at 15 × 15 mm². Each chip carries four groups with four identical transistors, with a channel length of 2.5, 5, 10 and 20 µm respectively. Identical layouts with graded channel widths as well as a flexible selection of the oxide thickness allow the adjustment to a broad voltage and conductivity range of the test materials. Customer-specific layouts with different electrode geometries are possible at any time.

OFET Miniprober

OFET miniprober
OFET miniprober

In order to simply and quickly measure OFET components with a given substrate size, pad grid and pad arrangement in large batches, Fraunhofer IPMS has developed a miniprober. It has two electric connections on the front (source and drain) and one connection on the back (gate) and does not require probe station, samplers or manipulator pins.

A reliable interconnection is established on contact pads, which are only 0.5 × 0.5 mm² in size. Customized versions of the miniprober varying the connection arrangement, the position and number of the pads are possible. This makes the miniprober suitable for other applications in addition to OFETs. Signals are transmitted to the measurement instrument by BNC or triax cables.

Advantages of the OFET Miniprober:

  • No probing system required
  • Easy DUT handling
  • Stable and secure connection
  • Other chip sizes or pad arrangements possible
  • Suitable for mobile applications
  • Small size