Analysis and Subsequent Optimization of a Microcontroller Program for precise control of Pneumatic Valves used for Hot Wire Chemical Vapor Deposition


1. Summer Internship (20.05.12 - 30.07.12)
By – Ashish Ranjan Jha (B.Tech, Elec. Engg., IITR)
At – Otto Von Guerick University, Germany

2. An introduction to Hot Wire Chemical Vapor Deposition
(HWCVD)
• Phase Change Memories (PCM)
• HWCVD of Ge2Sb2Te5 Thin Films
• Precursor operation
Operation of microcontroller controlled pneumatic valves
• Development board – making
• Development board – in synchronization with the microcontroller
• AVR Studio – overview
HWCVD Microcontroller Program
• Analysis
• Subsequent optimization

3.  The two distinct states pave the way for “binary
storage”
 Phase changed
 to crystalline – by crystallization (by applying an
electrical pulse to heat the cell to crystallization temp.)
 to amorphous – by quenching(melting) the cell
Crystalline
(Very low
resistivity)
Amorphous
(High
resistivity)
Phase change
material(Ge2Sb2Te5)

4. Better conformity and composition control than
conventional physical vapor deposition methods
Precursor activation by a hot wire within the CVD
process yields lower roughness and a better lateral
growth
Hot wire enables the use of a wider range of
precursors due to its catalytic character

6.  To deposit Ge2Sb2Te5, we require Ge, Sb and Te
precursors
 Each to be dosed to main carrier gas line
 Done via valves that open and close at defined
time intervals
 Carrier gas - N2 (usually)

8. Consisted of :
• 8 LEDSs
• 8 TACT Switches
• Two 8-pin female header
ports
It was meant to
simulate the valve
action
(opening and
closing) through
LEDs (blinking on &
off)
Making this board gave
opportunity to learn
soldering

10. Microcontroller used -
ATmega88
Programming
Board – AVR
Dragon
Programming
Environment –
AVR Studio
Connections were
made in Dragon
Board for In-System
Programming(ISP
mode)
A serial UART
connection was
established via the
RST-232 port

11. AVR Dragon Board (Front) (Rear)
Dragon board prototype area ZIF DIP pin socket

12.  Making the program,
compiling , debugging,
and burning it in the form
of machine language
onto the microprocessor
was all done in the AVR
Studio programming
environment
 It gave the ease of
programming in C
programming language

13. 
 This shows that on a program where port A data is input and its
data is copied to pin B which serves as output, changing the
contents of port A in debugging mode to 0x04 results in
corresponding expected change in port B status

14.  The written C – code
is compiled and once
free from errors, is
built into a .hex file (it
can be considered as
the AVR’s machine
language format)
 After that, the .hex file
is burnt onto the
AVR Dragon board
connected via USB

15. // oscillator at 1 MHz so the value is 1000000UL
#define F_CPU 1000000UL
include <avr/io.h>
#include <util/delay.h>
// LED is connected to PB4 (pin 3 on the chip)
#define LEDPIN 4
int main(void)
{
DDRB = 0x1F; // PB0-PB4 output
PORTB = 0x00; // Set all pins low
// Turn LED on for 1 sec and then off for 1 sec forever
while(1)
{
PORTB |= _BV(LEDPIN); // Turn LED on
_delay_ms(1000); // Wait 1000 ms (1 sec)
PORTB &= ~(_BV(LEDPIN)); // Turn LED off
_delay_ms(1000); // Wait 1000 ms (1 sec)
}
return 0;
}

16. Program for operating four precursor valves
as per defined opening, closing times and
number of cycles
Task was to analyze and debug the program
step by step by running the modules of
program on the development board
In the next slides are shown a few portions of
the 9 – pages long program.

17. ********************************************************************************
* Sending string format to MC(Microcontroller) :
* Ton1;Toff1;count1;Ton2;Toff2;count2;Ton3;Toff3;count3;Ton4;Toff4;count4;255
* __________‐‐‐‐‐‐‐‐‐__________‐‐‐‐‐‐‐‐‐__________‐‐‐
*
* <‐ Ton ‐><‐ Toff ‐><‐ Ton ‐><‐ Toff ‐><‐‐
*
* <‐‐‐‐‐cycle1‐‐‐‐‐‐><‐‐‐‐‐cycle2‐‐‐‐‐‐><‐‐
*
* Ton(x) ‐ valve(x) opening time ; Toff(x) ‐ valve(x) closing time ;
* count(x) ‐ valve(x) number of cycles.
*
* Ton,Toff,count ‐ in ASCII char ; 255 ‐ decimal.
********************************************************************************

18. * |Precursor number | Activate Input | Valve output |
* |_________________|________________|________________|
* | | SUB-D pin | MC | SUB-D| MC |
* | |__________|_____|______|_________|
* | 1 | 2 | PC1 | 18 | PB0 |
* | 2 | 5 | PC2 | 9 | PB1 |
* | 3 | 10 | PC3 | 17 | PB2 |
* | 4 | 20 | PC4 | 16 | PC0 |
* |_________________|__________|_____|______|_________|
* | ACK from PLC | | | | |
* | to MC | 1 | PD3 | -- | --- |
* |_________________|__________|_____|______|_________|
* | ACK from MC | | | | |
* | to PLC | -- | --- | 6 | PD7 |
* |_________________|__________|_____|______|_________|
* | GND | 11 | | | |
* | | 13 | GND | | |
* | | 15 | | | |
* |_________________|__________|_____|______|_________|

19. char decode(unsigned char *usart_buffer)
{
unsigned char i,s,j,temp; // initialize local variables
i=0;
j=0;
s=0;
int v=0, pow;
while((usart_buffer[i]!=255)) // 225 is the end value of the ASCII string
{
// other than 0,1,...9 and ; are not allowed.
if((('0' <= usart_buffer[i]) && (usart_buffer[i] <= '9')) || (usart_buffer[i] == ';'))
{
if(usart_buffer[i] != ';' ) // ";" is the separator for each value.
// decoding.
{
temp = usart_buffer[i] ‐ 48;
if(s=0) pow=1;
else pow=10;
v = (v * pow) +temp;
s++;
}
// copy values to character string if it finds ";" symbol.

20. else
{
a[j] = v;
j++;
v=0;
s=0;
if (j>11) j=0;
}
}
else
{
return 0;
memset(a, 0, 12); // RESET array a[]
break;
}
i++;
}
return 1;
}

21. 1. HWCVD, ALD, PSM, etc. topic were read from
research papers as the final task was related to it
2. Soldering was practiced and then the making of
the development board (which was made to
simulate the modules of the main program)
3. Familiarizing with AVR Dragon Board and
Atmega88 microcontroller

22. 4. Programming (simple programs) practice n AVR
Studio environment (to be able to analyze and
debug the main program)
5. Lastly, understanding step by step, the main
program(originally with no comments), adding
comments where ever necessary and
implementing each of its function and module in
the development board to verify the working and
some suggestions for optimization in the UART
serial communication

24.  G. W. Burr, B. N. Kurdi, J. C. Scott, C. H. Lam, K. Gopalakrishnan and R. S. Shenoy, “Overview of
candidate device technologies for storage-class memory”, IBM J. Res. Dev. 52, 449 (2008).
 D. Reso, M. Silinkas, M. Lisker, A. Schubert and E. P. Burte, “Hot wire chemical vapor deposition of
germanium selenide thin films for nonvolatile random access memory applications”, Appl. Phys. Lett.
98 (2011).
 D. Reso, M. Silinkas, B. Kalkofen, M. Lisker and E. P. Burte, “Hot wire chemical vapor deposition of
Ge2Sb2Te5 thin films”, J. Electrochem. Soc. 158 (2011).
 D. Reso, M. Silinkas, M. Lisker, A. Gewalt and E. P. Burte, “The role of hydrogen in hot wire chemical
vapor deposition of Ge-Sb-Te thi films”, Thin Solid Films 519, 2150 (2011).
 D. Reso, M. Silinkas, M. Lisker and E. P. Burte, “Growth of germanium sulfide by hot wire chemical
vapor deposition for nonvolatile memory applications”, Journal of Non-Crystalline Solids (2012).
 AVR Dragon reading manual
 ATmega 88 Datasheet - “Atmel AVR 8-bit microcontroller with 8K bytes In System Programmable
Flash”
 AVR Microcontroller Tutorials – www.mikrocontroller.net
 AVR Programming Discussion Forum – www.avrfreaks.net
 AVR Studio Instruction Manual