Summer 2025 CMU Update
This page contains information about the state of the ALD project as of August 2025. This is the most recent update for the project, and focuses on control systems + precursor handling.
Progress
Control Systems
Software
The ALD valves and heating elements were previously controlled through LabVIEW, but we have found it easier to use one main Arduino program loop to control both elements. Through the use of bang-bang controls, this program reads thermocouple values and uses them to actuate relays connected to heating elements in order to maintain a predetermined setpoint temperature. The heating elements include the substrate heater and heating tapes that control the temperature of the precursors and delivery line. This program is also responsible for actuating the ALD valves based on the number of pulses and duration of each of the pulses. For easier use, a GUI is being built to easily control all these factors. The instructions to use this program and GUI can be found in the controls folder of the ALD Github here.
As for the chamber pressure and carrier gas flow controls, protocols are still the same with manual control of both the throttle valve and mass flow controller (MCF).
Hardware
Since the Spring 2025 semester, there have been many changes to the hardware for the ALD. Starting with the Arduino stack, our current stack include the following:
Arduino Uno Rev3
4-channel k-type thermocouple sensor MAX31855 Arduino shield
4-channel j-type thermocouple sensor MAX31855 Arduino shield
Screw terminal block breakout shield
The Arduino stack, along with other electrical components, will be placed within a NEMA enclosure to ensure safe-handling of high currents and voltages in case of an electrical failure or accident.
The NEMA enclosure and wiring:
For the wires to run in and out of the enclosure safely, cable glands were used on the back and side of the enclosure.
The three ALD valve wires are each split into neutral and live wires that are extended to the blue and yellow wires that lead to the cable glands into the enclosure. The middle connection is through plugs that ensures electrical contact.
The heating tapes are to a male and female extension cable with the heating tape prongs going into the female end of the cable. The male end of the extension cable has been cut off and split based on the neutral and live wiring and wired into the 8-shield relay and bus bar accordingly.
Other Design Choices
We have changed the front panel of the chamber that previously had a glass window to one that is completely aluminum. The glass on the window would reach an unsafe temperature based on our operating conditions and wanted to minimize the amount of heat lost.
The thermocouple for the substrate heater has been switched to one that is coated with PFA which is compatible with the precursors and byproducts. This thermocouple uses j-type, so we bought the 4-channel j-type thermocouple sensor MAX31855 Arduino shield along with the j-type extender to the enclosure.
Precursor Compatibility Chart
(Only for certain precursors based on the oxide of choice)
Al2O3
Al2O3
Al2O3
ITO
ITO
ITO
ITO
ITO
Precursors/ expected byproducts
TMA
Water
Methane
TMIn
TDMASn
Water
Methane
Dimethylamine
HN(CH3)2
PVC
❌
✅
✅
❌
❌
✅
✅
❌
Polypropylene
❌
✅
✅
❌
❌
✅
✅
✅
Stainless steel
✅
✅
✅
✅
✅
✅
✅
✅
PLA
❌
✅
✅
❌
❌
✅
✅
❌
PETG
❌
✅
✅
❌
❌
✅
✅
❌
PFA
✅
✅
✅
✅
✅
✅
✅
✅
HfO2
HfO2
HfO2
ZrO2
ZrO2
ZrO2
Precursors/ expected byproducts
TDMAHf
Water
Dimethylamine
HN(CH3)2
TDMA-Zr
Water
Dimethylamine
HN(CH3)2
PVC
❌
✅
✅
❌
✅
❌
Polypropylene
❌
✅
✅
❌
✅
✅
Stainless steel
✅
✅
✅
✅
✅
✅
PLA
❌
✅
✅
❌
✅
❌
PETG
❌
✅
✅
❌
✅
❌
PTFE
✅
✅
✅
✅
✅
✅
PFA
✅
✅
✅
✅
✅
✅
Trap System
The company Mass-Vac has posi-trap vacuum traps that we will be using to trap the precursors and byproducts created from the process. There will be three 4” traps in sequential order with the following filter elements:
Ammoniasorb (for amines)
Activated charcoal (for organic vapors)
Stainless steel gauze (for condensable particles and oil vapors)
Note: You are able to choose between two models that can be more suitable for your set up, including a right-angle or straight-through shape for the posi-traps.
This trap system will be after the chamber and before the vacuum pump to prevent major damage on the pump and filter out the chemicals before entering the exhaust. To know when to switch the filter elements of the traps, you can put one pressure gauge on the inlet side and another on the outlet side of the trap configuration. When there is a significant pressure difference between the two gauges, it is a good indicator to switch out the filter elements.
***Add a picture of how our traps are set up***
Exhaust System
***Additional information on changes from the original layout***
The exhaust system is composed of aluminum and stainless steel to ensure safety and contain the gases to the vent. The following will be a list of components from the 6” vent outlet to the pump:
6” to 3” reducer
...
Process Parameters
Hafnium oxide (HfO2)
Component
Value
Sources
Number of cycles
(Variable)
N/A
Substrate heater temperature (ºC)
85 to 350 (above 200 decrease purge time to 5 seconds)
275 to 300
Bubbler temp. for TDMAHf (ºC)
75 or 80
Bubbler temp. for H2O (ºC)
25 (room temp. should be fine?)
Zirconium oxide (ZrO2)
Component
Value
Source
TDMAZr pulse time (s)
0.03
H2O pulse time (s)
0.015
Purge time (s)
10 to 30
Number of cycles
100 to 300
Substrate heater temperature (ºC)
100 to 275
Bubbler temp. for TDMAZr (ºC)
75
Bubbler temp. for H2O (ºC)
25 (room temp. should be fine?)
Valve line temp. (ºC)
90
Chamber pressure (mTorr)
300 to 400
Aluminum Oxide (Al2O3)
Component
Value
Source
Bubbler temp. for TMA (ºC)
25 (room temp. should be fine?)
Bubbler temp. for H2O (ºC)
25 (room temp. should be fine?)
Valve line temp. (ºC)
150
ITO
Component
Value
Sources
N2 carrier gas flow rate (sccm)
100 (40 in the paper)
H2O pulse time for TDMASn (s)
1
H2O pulse time for TMIn (s)
0.75
Number of cycles
(Variable)
N/A
Substrate heater temperature (ºC)
225
Bubbler temp. for TDMASn and TMIn (ºC)
60
Bubbler temp. for H2O (ºC)n
25 (room temp. should be fine?)
Valve line temp. (ºC)
110
***Check below
***Valve line temp. for ITO
This article deposits tin oxide, keeping the TDMASn bubbler at 40 ºC and the tubing for that connection at 150ºC to prevent condensation to the chamber walls.
This source states that TMI decomposition in the gas phase is feasible at T = 120–535 °C in an N2 environment.
This source states that a temperature range of 70–150 °C will volatilize around 92% of the TDMASn. Above 150 °C but below 230 °C, TDMASn is easily volatilize. 230 °C is when TDMASn starts to decompose.
Testing
Chamber pressure
(Link to google docs/sheets data)
Heating elements
(Link to google docs/sheets data)
Bill of Materials (Controls, Trap, Exhaust)
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