1. MICROELECTROMECHANICAL SYSTEMS ( MEMS )
HARIKRISHNA SATISH.T

2. Introduction:
MEMS stands for Micro-electromechanical systems, a manufacturing technology that enables the development of electromechanical systems using batch fabrication techniques similar to those used in integrated circuit (IC) design.
They can range in size from micrometers to millimeters
MEMS integrate mechanical elements, sensors, actuators and electronics on a silicon substrate using a process technology called micro fabrication.
Micro electro mechanical System (MEMS) is making and combining of miniaturized mechanical and electrical components on a common silicon substrate through micro fabrication technology.

3. How MEMS work?
The sensors gather information by measuring mechanical, thermal, biological, chemical, magnetic and optical signals from the environment.
The microelectronic Ic’s act as the decision-making piece of the system, by processing the information given by the sensors.
Finally, the actuators help the system respond by moving, pumping, filtering or somehow controlling the
surrounding environment to achieve its purpose.

4. Manufacturing process:

5. What is Micromachining ?
The MEMS materials:
Primarily silicon its compounds
other materials are quartz crystal, glass, metals such as aluminum, titanium, tungsten and copper
polymers such as photo resist.
What is Micromachining ?
Micromachining is a parallel (batch) process in which dozens to tens of thousands of identical elements are fabricated simultaneously on the same wafer.
Divided into three major categories: basic, advanced, and nonlithographic processes.

6. Basic process flow in micromachining:
Figure : Illustration of the basic process flow in micromachining: Layers are deposited; photoresist
is lithographically patterned and then used as a mask to etch the underlying materials. The
process is repeated until completion of the microstructure.

7. MICROELECTROMECHANICAL SYSTEM
BASIC PROCESS TOOLS Deposition Process Epitaxy: Epitaxy is a deposition method to grow a crystalline silicon layer over a silicon wafer, but with a differing dopant type and concentration
Impurity dopants
[AsH3 ; PH3]
(Controlled)
MICROELECTROMECHANICAL SYSTEM
Silicon Contain source gas
[SiH4/SiCl4/SiH2Cl2]
High Temperature
( )
[Controlled]
Wafer Scale p-n junction for
Controlled electrochemical etching

8. Oxidation: High-quality amorphous silicon dioxide is obtained by oxidizing silicon in either dry oxygen or in steam at elevated temperatures (850º–1,150ºC)
Si + O2/ Steam SiO2
It is Depend on Temperature , Oxidizing environment and Time.
Sputter Deposition:

9. Condenses on a substrate
Evaporation
Heated at high Temperature
(Scanning at high voltage electronic beam)
(Water cooling of the target and
shielding from X-ray)
Al , Si, Ti,Cr , Al2O3
Evaporation
Condenses on a substrate
to form a film

10. CVD (Chemical Vapour Deposition)
Deposition Of Polysilicon :-
SiH Si H2
Polysilicon may be grown directly with doping.
Deposition of Silicon dioxide :-
SiH O SiO H2
SiCl2H N2O SiO N HCl
Si(OC2H5) N2O SiO byproduct
25 p.a -150 p.a
In CVD Chamber
High temperature
Oxide
Doped
Semiconductor
Impurity
P2O5

11. Deposition of Silicon Nitrides
3SiH NH Si3N H2
3SiCl2H NH Si3N HCl H2
2SiH N SiNH H2
SiH NH SiNH H2
Silicon nitride is common in the semiconductor industry for the passivation of electronic devices because it forms an excellent protective barrier against the diffusion of water and sodium ions

12. Photolithography Photosensitive material Selectively expose to Light
Non-exposed part
(remain same in physical properties)
Exposed part
(physical property change)
Perform Etching
Deposition of metal or
other thin film deposition

13. Crystallographic orientation
Etching: In etching, the objective is to selectively remove material using imaged photoresist as a masking template.
Wet Etching :-
Anisotropic Wet Etching:
Dipped into
Removal of material
Depending on the
Crystallographic orientation
Substrate
KOH Solution

14. Electrochemical Etching

15. Reactive Ion Etching ( RIE )
Process of reactive ion etching.
Placed into
Substrate
Reactor
contain
several
gas
Plasma is struck in the mixture
Gas molecule into ions
React with the surface
of the material and etched

16. Deep Reactive Ion Etching ( DRIE )
SF6 isotopic Etching
(SF6 & O2 etches the substrate)
C4F8 deposition
SF6 anisotropic etching
for floor cleaning

17. Using these processes some micromachining methods are applied on silicon materials are:
A) Bulk micromachining: Bulk micromachining designates the point at which the bulk of the Si substrate is etched away to leave behind the desired micromechanical elements. The methods commonly used to remove excess material are wet and dry etching, allowing varying degree of control on the profile of the final structures.
B) Surface Micromachining: The MEMS fabrication process based on standard CMOS microelectronic processes. MEMS structures are photo lithographically patterned in alternating layers of deposited polysilicon and silicon dioxide, and then are "released" by dissolving away the silicon dioxide layers.

18. Applications of MEMS : inkjet-printer cartridges, accelerometer,
miniature robots,
micro engines,
inertial sensors,
micro actuators,
optical scanners,
fluid pumps,
chemical, pressure and flow sensors.
Application in Radio frequency (RF)

19. Reference :- By Maluf Nadim and Williams Kirt .
An Introduction to Microelectromechanical Systems Engineering.
By committee on Advanced Material and Fabrication.
Microelectromechanical Systems.
The MEMS Handbook.

20. Thank You