Ossila Test Chips Low Density User Guide

: June 13, 2024
: Ossila

Table of Contents

Ossila Test Chips Low Density
Product Information
Overview
Substrate Preparation
Evaporation Preparation
Evaporation
Quality Check
References
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Ossila Test Chips Low Density

Product Information

The OFET Test Chips are low-density test chips designed for fabricating organic field-effect transistors (OFETs) using Ossila’s deposition mask. These test chips enable scientists to study and analyze the performance of OFETs in a controlled environment. The
fabrication process should be carried out in a clean environment to prevent any particulates or dust from causing shorting of the OFET channels.

Requirements

Tweezers
Substrates rack
Cleaning beaker
Glassware
Acetone
IPA (Isopropyl Alcohol)
N2 gun (for blow drying)
DI water
Screws and nuts

OFET Test Chips: Product Usage Instructions

Substrate Preparation

Ensure that tweezers, substrates rack, cleaning beaker, and all glassware are properly cleaned.
Use a dedicated crystallizing dish (glass beaker) for each step of the cleaning routine.
Rinse the tweezers with acetone, IPA, and then blow dry with N2 gun.
Separate the desired number of substrates from the silicon wafer.
Load the substrates into a substrate rack, ensuring that all substrates have the mirror-polished side facing the same direction.
Note the direction to avoid touching the mirror-polished side when moving the rack.

Evaporation Preparation

Before proceeding with evaporation, ensure that the deposition mask is free of dust or residue, and that all its features are undamaged. Assemble the evaporation stack in the following order:

Deposition mask support
Deposition mask
Substrate holder

Deposition Mask Cleaning

If the deposition mask is not clean, follow these steps to clean it:

Fill a large beaker with DI water.
Assemble the stack as mentioned above (deposition mask support, deposition mask, substrate holder), and loosely fasten together with screws and nuts.
Immerse the mask in the water for 1 minute, gently moving it up and down.
Repeat the process with acetone and IPA.

Manual version: 1.0.D

Overview

This guide contains instructions for fabricating low-density OFET test chips using Ossila’s deposition mask for low-density OFETs. Fabrication should be performed in a clean environment, if possible, as small particulates or dust can cause shorting of the OFET channels.

Requirements

Silicon oxide substrates (S146 / S148)
Tweezers (C121)
Substrate rack for cleaning and storage (E101)
Annealing and cleaning beaker (C191)
Hellmanex III for critical cleaning (C141)
Ultrasonic cleaner
Source-drain deposition mask for low density OFETs (E291 / E292)
Evaporation stack – low-density OFETs (E281)
Thermal evaporator
De-ionised (DI) water
Chromium and gold evaporation sources

Substrate Preparation

Make sure that tweezers, substrates rack, cleaning beaker, and all glassware are properly cleaned.
Use a dedicated crystallising dish (glass beaker) for each step of the cleaning routine.
Rinse the tweezers with acetone, IPA and then blow dry with N2 gun.
Separate the desired number of substrates from the silicon wafer.
Load the substrates into a substrate rack, making sure that all substrates have the mirror-polished side facing the same direction.
Keep note of this direction so to avoid touching the mirror-polished side when moving the rack.

Substrate Cleaning

Sonicate in hot (70 – 80 °C) 1% Hellmanex III solution for 5 minutes.
Rinse thoroughly twice in hot DI water.
Sonicate in IPA for 5 minutes.
Rinse thoroughly twice in cold DI water.
Store in cold DI water (for up to 12 hours) until ready to load into the evaporation stack.

Evaporation Preparation

Check that the deposition mask is free of dust or residue, and that features are undamaged. Assemble the evaporation stack in the following order:

Ossila-Test-Chips-Low-Density-fig-1

Deposition Mask Cleaning

If the deposition mask is not clean, use the following routine to clean it:

Fill a large beaker with DI water.
Assemble the stack as above (deposition mask support, deposition mask, substrate holder), and loosely fasten together with the screws and nuts.
Immerse the mask in the water for 1 minute, gently moving it up and down.
Repeat with acetone and IPA.
I. If necessary, an ultrasonic cleaner can be used.
Leave at room temperature to dry.
Check that mask features have not been damaged by the cleaning routine.

Loading Substrates

Using tweezers, take a substrate and blow dry it using N2.
Ensure the entire substrate is dry, including the back and edges.
Try to avoid touching areas of the substrate where deposition will occur.
Carefully place the substrate into one of the slots of the substrate holder.
Once all substrates have been loaded, carefully place the lid on top of the evaporation stack.
Add the nuts to the screws and gently tighten them to fasten the stack together.
Place the magnetic sheet on the back of the lid.

Evaporation

Load the evaporation stack, chromium source, and gold source into the evaporator and pump it down to typical evaporation pressure.
If available, start the evaporation stack rotation.
Evaporate 1 – 2 nm of chromium.
Note, chromium forms a layer of chromium oxide on its surface. This will cause an increase in pressure as it heats up. Deposition of chromium should not be started until the pressure returns to normal, indicating this layer has been removed.
Wait 5 – 10 minutes for the chromium to cool.
Deposit 60 – 70 nm of gold.
Wait 5 – 10 minutes for the gold to cool.
7. Vent the evaporator and remove the evaporation stack.

Quality Check

To check that the test chips have deposited correctly, they can be inspected with a microscope and a multimeter.
When inspected under microscope the channels should be well defined, with nothing bridging the gap between the source and drain electrodes, as shown in Figure 5.1 below. Additionally, a multimeter can be used to check that there is no electrical connection between the source and drain electrodes.

If any dust or particulate is seen or an electrical connection measured, first try using N2 to remove it. If that does not work, try to gently clean the channel using IPA and a cotton bud or cleanroom paper.
The quality of the gate electrodes can be checked using a multimeter. Simply place a probe on each of the gate electrodes and measure the resistance. It should be no higher than a few 10s of Ohms.

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