Silicon Programming--Introduction to MEMS 1 Interfacing--MEMS; energy domains; mechanical and...

Silicon Programming--Introduction to MEMS

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Interfacing--MEMS;

energy domains; mechanical and fluidic devices


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MEMS (Microelectromechanical systems)

(Other commonly used terms: Microsystems (Europe); Microfluidics;Mechatronics (Japan) )

All these terms refer to "systems" incorporating electrical elements and elements from other domains into a "chip" or "integrated circuit". Both miniaturization and integration are usually implied.

Another term commonly used is "SOC", which stands for "system on a chip".


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Motivations for MEMS:

-----space (area) savings

-----power reduction (can we use batteries?)

-----portability (reduced weight / power)

-----reliability--because of integration

-----economic savings--"mass produce" elements as VLSI chips are

currently produced

-----application of well-understood VLSI processing techniques to other domains


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Application areas (a sampling)--

-----automotive systems

-----environmental control / monitoring

-----health care

-----defense systems

----- automated manufacturing

Example applications (see, e.g., Analog Devices website, www.analog.com)::

--airbags: change in acceleration (force) is translated into signal to deploy airbag --navigation and stabilization: micro gyroscopes provide a frame of reference in navigation and stabilization systems in cars, planes, etc.--”lab on a chip”: biological / chemical procedures can be carried out on one integrated chip (Lab on a Chip journal: http://www.rsc.org/is/journals/current/loc/locpub.htm)


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Area is INHERENTLY MULTIDISCIPLINARY (based on today's "disciplines")

How old is this area? (~ 30 years)

basic reference:K. Petersen, Silicon as a mechanical material, IEEE Proceedings 70 (5), May 1982, 420-457.


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Basic idea: IC's perform (electronic) calculations extremely well; I/O is NOT generally in the electrical domain--how can I/O elements (“sensors” and “actuators”, or "transducers")be integrated?


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Energy Domains:

1. thermal--temperature, heat, heat flow, etc.

2. mechanical--force, pressure, ve;ocity, acceleration, position, etc.

3. chemical--concentration, material composition, reaction rate, etc.

4. magnetic--magnetic field intensity, flux density, magnetization, etc.

5. radiant--intensity, wavelength, polarizaion, phase, etc.

6. electrical--voltage, current, charge, etc.


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Relation to IC's:

Typical IC is built up of "layers" of material. These layers can be used to make other devices, e.g., cantilever beams for sensing and actuating

Techniques for "machining" are those used in IC fabrication--how

can they be used / modified to make devices usable in other domains?


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Devices are generally divided into two classes according to processing required:

a. "surface micromachining" (2.5D devices)

uses “layers”

b. "bulk micromachining"

(true 3D devices)


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examples:

beams

cantilever beams

membranes

ducts

motors, movable partshttp://www.sfu.ca/immr/projects/ensc494-01/acoppin/designs.html


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How can MEMS development make use of well-understood IC CAD capabilities?What extensions are needed for CAD for MEMS?

Recall:

1. Predicting IC performance requires input from fabrication, design, and environment.

2. Tools for incorporating information from each of these domainsare necessary for "rapid prototyping" which make manyIC designs economically feasible.


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Comparisons of Mechanical Properties (Petersen)Property Si SiO2 Steel Al

Yield(1010 dyne/cm2) 7.0 8.4 4.2 0.17

Hardness(kg/mm2) 850 820 1500 130

Young's mod(1012dyne/cm2) 1.9 0.73 4.9 0.7

Density(gr/cm3) 2.3 2.5 7.9 2.7

Therm. cond(W/cmoC) 1.57 .014 0.97 2.36

Thermal exp(10-6/oC) 2.33 0.55 12 25


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Tasks: Specify-Design-Simulate-Fab-Test-Maintain=====================================================================================LEVELS|| VIEWS || Behavioral Structural Physical=====================================================================================4 || Specifications, CPUs,Memory, Partitions || Systems Switches, Complex || MEMS------------------------------------------------------------------------------------------------------------------------------------------------3 || Algorithms Data Structures Clusters------------------------------------------------------------------------------------------------------------------------------------------------2 || Register Transfers ALUs, Registers, Floorplans || Electromechanical || Components----------------------------------------------------------------------------------------------------------------------------------------------- 1 || Boolean Equations,

Gates, Flip-flops, Cells, || FSMs, Mechanical Sensors, Actuators Modules || Behavior -----------------------------------------------------------------------------------------------------------------------------------------------0 || Transfer Functions Transistors, Wires, Layout || Contacts, Vias, Geometry || Beams, Membranes, || Holes, Grooves, || Joints====================================================================================


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Cantilever beam--static and dynamic behavior; extending VHDL to other domains (VHDL-AMS)


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We will look at how a cantilever beam is built in a “typical” MEMS process--the “MUMPS” process (MultiUser MEMS Process)

there are two structural (polysilicon) layers. Structures can be made of: first poly by itself, second poly by itself, first poly-second poly together.

typical layer thickness: ~ 2 microns--"large" (compared to today's circuit elements)


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cantilever beam-side view cantilever beam-top view

height (h)

length (l)

thickness (t)

width (w)

u

displacement (x)

length (l)

Simple cantilever beam, height h, length l, width w, thickness t. If the beam is made of a material with density p and Young’s modulus E, then mass m and moment of inertia I are given by:

m = pwtl I = (wt3) / 12

If u = distance from the beam's anchor to its end, 0 <= u <= l, and force F(u) is applied at point u, the beam will be displaced a distance x(u). What is x(u)?


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If a constant force F is applied to the free end of the beam, then its maximum (static) deflection is given by standard equation for a maximum deflection of a cantilever beam of constant cross section :

where D is the deflection of the free end of the beam, F is the force applied to the free end, L is the length of the beam, and EI is the flexural rigidity of the beam (E = Young's modulus).

EI

FLD

3

3


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If F varies with respect to time s, then we actually have F = F( s,u) and we seek the dynamic solution x = x(s,u).


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Method 1. The cantilever beam as a spring. Assume F is a function of time s alone, applied at the free end of the beam.

F = m x ' ' + B x ' + kx,where the spring constant k is given by k = (3EI) / (L3)and the damping coefficient B is given (experimentally) byB = 2*((mk)1/2) / 5.


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F = m x ' ' + B x ' + kx

can be translated into the electrical domain:

I = C V ' + (1/R) V + (1/L)V(y)dy

where I = current, C = capacitance, R = resistance, L = inductance, V = voltage.(This represents a circuit with R,C,L in parallel). So if we use this form of the equation we can simulate the behavior of the beam using SPICE.


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Method 2. Finite element analysis.

This is a standard method for dealing numerically with complex systems. Here we can break the beam into sections and model the behavior of each section, keeping them "tied" together at the ends. This allows us to deal with a force which varies along the beam length.


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A beam-capacitor system. By adding an insulated plate on the base for the beam, we can create a capacitor. Here the distance (h - x in the equation above, if we ignore the plate height) is the distance between the two capacitor plates. The equation for the attractive force at the end of the beam is:

F = (AE0V2) / (2y2),where A is the area of the capacitor plate, V is the voltage, E0 is the permittivity of air (=8.85 x 10-12), and y is the distance between the two plates.


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example: VHDL-AMS (VHDL with Analog and Mixed Signal extensions) model of cantilever beam:

entity cantbeam isend entity cantbeam;

architecture simple of cantbeam is quantity x: real;quantity v: real;quantity a: real;quantity F: real;constant L: real := 20.0E-6;constant W: real := 10.0E-6;constant H: real := 1.5E-6;constant P: real := 2.26E3;constant M: real := L*W*H*P;constant Y: real := 170.0E9;constant IZ: real:= (W*H*H*H)/12.0;constant Rigidity: real := Y*IZ;constant k: real := (3.0*Rigidity)/(L*L*L);constant B: real := 0.4*sqrt(M*K);begin.b1: break v => 0.0, a => 0.0, x => 0.0, F => 0.0; force: F == F1 + F2 + F3;force1: F1 == M*a;force2: F2 == k*x;force3: F3 == B*v;vel: v == x'dot;accel: a == v'dot;end architecture simple;

Equations

Declarations


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Cantilever beam actuator:

entity cantbeamactuator is

port(Vin,Length,Width: in real;deflection,Force: out real);end entity cantbeamactuator;

architecture simple of cantbeamactuator isquantity x: real;quantity Volt: real;quantity v: real;quantity a: real;quantity F: real;quantity L: real;quantity W: real;quantity H: real;quantity M: real;quantity IZ: real;quantity Rigidity: real;quantity k: real;constant P: real := 2.26E3;constant Y: real := 170.0E9;constant Eo: real:= 8.85E-12;constant H: real := 1.5E-6;begin

Initialize: Process (Vin,Length,Width)VARIABLE MASS,MOMENT,RIG,SpringK: real;BEGIN

Volt := Vin;L := Length;W := Width;MASS := L*W*H*P;M := MASS;MOMENT := (W*H*H*H)/12.0;IZ := MOMENT;RIG := Y*IZ;Rigidity := RIG;B := 0.4*sqrt(M*K);SpringK := (3.0*Rigidity)/(L*L*L);k := SpringK;

END process;Calc_Force: Process

VARIABLE Area, Perm,AttractForce: real;BEGIN

Area := L*W;Perm := Eo;AttractForce:= (Area*Perm*Volt*Volt)/(2.0*x*x);F := AttractForce;

END process;Force_applied: F == F1 + F2 + F3;force1: F1 == M*a;force2: F2 == k*x;force3: F3 == B*v;vel: v == x'dot;accel: a == v'dot;deflection = x;Force = F;end architecture simple;

b1: break Volt => 0.0, a => 0.0, x => 0.0, F => 0.0; InputTestBench: Process

File Infile : text OPEN READ_MODE IS "cantbeam.in";VARIABLE linebuf : line;VARIABLE vtemp,ltemp,wtemp,htemp :real;BEGINWHILE (NOT (endfile(Infile))) LOOPreadline(Infile,linebuf);read(linebuf,vtemp);Vin <= vtemp; read(linebuf,ltemp);Length <= ltemp; read(linebuf,wtemp);Width <= wtemp; WAIT FOR 100 ns;END LOOP;END process;

Silicon Programming--Introduction to MEMS 1 Interfacing--MEMS; energy domains; mechanical and...

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