Recent Advances in Mechatronics - Ryszard Jabonski et al (Eds) Episode 2 Part 4 pot

Calibration of normal force in atomic force microscope M.. Unfortunately load applied during tests performed on the AFM such as: force – distance – curve measurement, wear and friction

Fig 5 Random-telegraph-signal observed for the dark and

light-illuminated conditions The frequency of the RTS

in-creases with decreasing wavelength This current switching

in RTS is ascribed to individual photon absorption

In order to improve the quantum efficiency, we have tried to detect photons absorbed in the underlying Si substrate by changing the substrate structure from n+-Si to p on p+ layered one As a preliminary result, we succeeded in detecting individual boron ions by monitoring the single-hole-tunneling current [9]

References

[1] D V Averin and K K Likharev, Single charge tunneling, edited by H

Grabert and M Devoret (Plenum, New York, 1992)

[2] L J Geerligs, V F Anderegg, P A M Holweg, J E Mooij, H ier, D Esteve, C Urbina, and M H Devoret, Phys Rev Lett 64, 2691 (1990)

Poth-[3] H Pothier, P Lafarge, C Urbina, D Esteve, and M H Devoret,

Euro-phys Lett 17, 249 (1992)

[4] H Ikeda and M Tabe, J Appl Phys 99, 073705 (2006)

[5] D.Moraru, Y.Ono, H.Inokawa, and M.Tabe, unpublished

[6] R.Nuryadi, H.Ikeda, Y.Ishikawa, and M.Tabe, IEEE Trans

Calibration of normal force in atomic force

microscope

M Ekwińska, G Ekwiński , Z Rymuza

Warsaw University of Technology, Institute of Micromechanics and Photonics,

pa-of this method also method for stiffness measurements pa-of MEMS structures was proposed

1 Introduction

Atomic force microscope (AFM) is one of the most commonly used vices for investigation of the tribological properties of the material in mi-cro and nanoscale This information is essential especially when construc-tion of the MEMS (Micro Electro Mechanical Systems) is taken into ac-count Unfortunately load applied during tests performed on the AFM (such as: force – distance – curve measurement, wear and friction tests) is given in arbitrary units In order to change qualitative information about applied load into quantitative information a calibration of the normal force has to be done

de-2 Theoretical approach

In order to determine real values of the load applied during test performed

on the AFM the calibration of the normal force has to be done There are many different calibration methods which are described elsewhere [1 – 11] In some of those methods only geometrical parameters of cantilever are needed In other methods the way of laser beam is analyzed and out of these information the stiffness of cantilever is established Using already established stiffness of cantilever, normal force applied to the system is established

In all cases the biggest problem is connected with high inaccuracy of the method and with considering machine stiffness Under these circumstances there still was a need to make a new approach to the normal force calibra-tion in the AFM In this paper a new easy- to – operate approach to the problem of normal force calibration was proposed and a new method of normal force was created The method is called Black Box Method In this method a whole measuring path of normal force is treated as a black box to which a known parameter is introduced Then a reaction of the AFM on the introduced parameter is being observed In other words the idea of the calibration is to cause the change of the normal force signal in arbitrary units by introducing to the system a known parameter (force) The intro-duced parameter is known value of force, which is applied at the very end

of the cantilever’s tip This causes displacement of the cantilever’s surface from which laser beam is reflecting The change of the reflection angle causes the change of the normal force signal in arbitrary units [a.u.]

Fig.1: System for calibration of normal force in AFM, 1 – area where AFM’s tip stands during calibration, 2 – plane which is elastically deformed during cali-

bration, 3 – holder of device

In order to calibrate normal force, a system with elastic element was rated [12, 13] (Fig.1.) There are three main parts of the elastic element: surface on which cantilever’s tip is located (1), flat surface with known

elabo-2

13

506 M. Ekwińska, G. Ekwiński, Z. Rymuza 

stiffness (2), surface to which AFM table is mounted (3) During tion of the AFM with this calibration device it is placed on the AFM table and cantilever’s tip is approached to the surface (1) After obtaining con-tact a force distance curve can be performed During the experiment the surface (1) is pushed by the cantilever what causes the deformation of the surface (2) The deformation is registered Bending of the cantilever as well as bending of the calibration device can be established Then the nor-mal force can be counted out of the deformation of the calibration device and stiffness of the surface (2) The ratio of the normal force estimated after calibration and the normal force in arbitrary units is the factor be-tween arbitrary units and real units

calibra-On the basis of this calibrating method a method for investigation of ness on MEMS structures, such as beams and bridges was created The test

stiff-is performed in the same scheme as the calibration procedure The only differences are: the use of a cantilever without tip (in order not to damage investigated structures) and the fact that cantilever has earlier established stiffness During this investigation the tip is approached to the investi-gated structure After reaching the structure’s surface the tip is pushed in order to achieve elastic deformation of the investigated structure Then the tip is withdrawn The result of the measurement is a force distance curve with additional bending on the approaching part

3 Experimental details

The investigations were divided into two sections First section was voted for checking a normal force calibration method The second one was usage of a new measuring technique for investigation of stiffness of MEMS structures

de-Both investigations were carried out under laboratory conditions: ture 22  0.5 °C, humidity 40 ± 2 %, atmospheric pressure, air atmosphere

tempera-In first step the calibration gratings were elaborated (Fig.2) Then a bration device for calibration of these gratings was built Using this cali-bration device the stiffness of the calibrating gratings was established

cali-Fig.2 Different geometries of calibration gratings

507 Calibration of normal force in atomic force microscope

After that set of cantilevers, which parameters are presented in Table 1 was calibrated

In the second step already calibrated cantilevers were used for the tion of stiffness of MEMS structures (microbridges and microcantilevers) During these measurements MikroMasch cantilever NSC12 type tip B was used It’s parameters are presented in Table.1

calibra-Table.1 Information about investigated AFM cantilevers according to producer ;

“+” cantilever with tip, “-” cantilever without tip

4 Results and conclusions

The stiffness of calibration gratings was established using Black Box Method The results of the calibration of MicroMasch cantilevers are pre-sented in Table 2

Table 2 Comparison of established stiffness for investigated cantilevers; k –

typi-cal stiffness given by producer, ∆k – interval between the biggest and the smallest

value of the stiffness (given by manufacturer), k E –stiffness established using calibration gratings, ∆ k E – inaccuracy of the estimation of stiffness using calibra-

Denotation of cantilever k [N/m] ∆k [N/m] kE [N/m] ∆kE [N/m] NSC12 cantilever E 0.3 0.1 – 0.4 0.33 ±0.03 CSC37 cantilever B 0.3 0.1 – 0.4 0.34 ±0.03 CSC37 cantilever B 0.3 0.1 – 0.4 0.15 ±0.02 NSC12 cantilever F 0.65 0.35 – 1.2 0.42 ±0.04

NSC12 cantilever B 14.0 6,5 – 27.5 13.4 ±1.35

508 M. Ekwińska, G. Ekwiński, Z. Rymuza 

Stiffness of MEMS structures established using calibration gratings is sented in Table 3

Table 3 Comparison of established stiffness for investigated MEMS structures;

k –stiffness established, ∆ k – inaccuracy of the estimation of stiffness ; C –

canti-lever like structure, materials out of which structures were made: first batch of devices are surface micromachined from 1.0µm thick cold-sputtered aluminium; polyimide film is used as a sacrificial layer; this gives an airgap of approximately 1.5-2µm, bottom metallisation layer is 0.5µm thick aluminium/1%silicon, covered

by a 100nm thick layer of PECVD silicon oxide

Results of the investigations proved that presented method is easy to ate Investigations were held on two different AFM microscopes and nearly the same results were achieved The method enables also to esti-mate stiffness of cantilever, which is more precise than information given

oper-by manufacturer of the cantilevers In this case also stiffness measurement

of the same cantilever were done on two different AFM microscope and results of the establishment were close to each other Under these circum-stances it can be said that proposed method of calibration of normal force

is correct

This method is also good for establishing stiffness of other MEMS tures (e.g .microbridges , microcantilevers) Especially when it is hard to establish stiffness because of structure is multiplayer one and the thickness

struc-of it is not known preciselly

[7] E L Florin, V T Moy, H E Gaub, Science 264, (1994), 415

[8] M Radmacher, J P Cleveland, P K Hansma, Scanning 17, (1995),

117

[9] R W Stark, T Drobek, W M Heckl, Ultramicroscopy 86, (2001), 207 [10] Ch T Gibson, G S Watson, S Myhra, Nanotechnology 7, (1996),

259 – 262

[11] N A Burnham, X Chen, C S Hodges, G A Matei, E J Thoreson,

C J Roberts, M C Davies, S J B Tendler, Nanotechnology 14, (2003), 1 - 6

[12] M Ekwińska, Z Rymuza, Tribologia, No5/2006, (2006), 17 - 27 [13] M Ekwińska, Z Rymuza, International Tribology Conference AU-STRIB 2006, 3-6 December Brisbane Australia., Proceedings on CD, Brisbane 2006

510 M. Ekwińska, G. Ekwiński, Z. Rymuza 

Advanced Algorithm for Measuring Tilt with

1 Introduction

The problem of determining tilt by means of a miniature sensor built of accelerometers belonging to Micro Electromechanical Systems (MEMS), characterized by miniature dimensions, satisfactory metrological parame-ters, and low cost, has been presented in detail in [1], while a way of in-creasing accuracy of the related measurements has been described in [2]

As far as mechatronics is concerned, the most typical applications of the considered sensor are control systems of mobile microrobots [3]

2 Calculating the tilt

An arbitrary tilt angle ϕ can be defined as two component angles α1 and

β1[1] (called pitch and roll), determined according to [2]:

2 2 1

z y

x

g g

g arctan

+

=

2 2 1

z x

y

g g

g arctan

+

=

where: g – gravitational acceleration; g x , g y , g z – component accelerations

3 Calibration of the tilt sensor

In order to apply a MEMS accelerometer it is often required to have it calibrated beforehand, as in the case of sensors presented e.g in [4] While building a dual-axis tilt sensor one must use either one tri-axial or multi-axial (such as e.g in [5]) accelerometer, two two-axial, or three uni-axial accelerometers Each accelerometer must be calibrated, preferably while embedded into the structure of the tilt sensor Then, it is possible to determine two essential parameters of the analog output signal generated

by the calibrated accelerometer: the offset and the gain (amplitude) Using the simplest way of calibrating tilt sensors it is possible to obtain their op-erational characteristics represented by the following formulas [6,7]:

1sin α

x x

where: U x z – voltage signal related to axis x z; a x z and b x z – offset and

amplitude of the respective signal U x z

The calibration process makes it also possible to evaluate uncertainties of determining the tilt angles by the way of defining appropriate prediction

intervals assigned to the variables U x z in equations (3)–(5) [6], whose maximal values ∆Ux z are used in the considered algorithm

4 Algorithm for determining tilt angles

Values of the parameters a x z and b x z obtained in the calibration process are indispensable during a standard operation of the tilt sensor In order to determine the tilt angles it is advantageous to use equations derived from:

z x z

x

z x z x z

b

a U g

After a readout of the output voltages U x z of the sensor it is possible to verify correctness of its indications, i.e to check whether it is affected by any external constant acceleration If that is the case, it is impossible to determine the tilt properly [1], as the gravitational acceleration geometri-cally sums up with the mentioned acceleration (variable accelerations can

be eliminated by appropriate filtering the output voltage of the ter) Then, the geometric sum of the Cartesian component accelerations

accelerome-has a value other than 1g When the gravitational acceleration affects the

sensor exclusively, the following idealized relation is true:

g g g

(7)

However, it is highly probable that the occurrence of random errors will result in a situation where the formula (7) is not satisfied [8] So, one should take into account the mentioned above errors ∆U x z determined while calibrating the sensor Under a rational assumption that their values will be approximately the same for each sensitive axis, and equal to ∆U, the correct indications of the sensor can be found within the following in-terval (assuming a statistical character of the regarded errors):

U m

m m

For instance, an acceleration with the absolute value of 2g, acting upwards

vertically, yields a resultant acceleration, indicated by the tilt sensor, that satisfies the inequality (8), yet has the sense opposite with respect to the gravity vector (the respective indication error reaches then the possibly highest value of 180°)

If one has no additional knowledge about the accelerations affecting the sensor, or about the real position of the sensor with respect to gravity, it is impossible, in a general case, to state whether its indications are correct However, if we are sure that no constant accelerations act, the inequality (8) may be disregarded

Yet, there is one more case to be considered Values of the parameters mx z

determined according to formulas resulting from (6) should be contained within the range of sine function, i.e 〈-1; 1〉 However, some random er-

513 Advanced algorithm for measuring tilt with MEMS accelerometers

rors may cause them to slightly exceed this interval, so in the further steps

one should use new variables n x z defined by relations derived from:

x

z x z

x

m n

m

n m

(9) Having verified correctness of the sensor indications and eliminated the case defined by (9), it is possible to determine values of the tilt angles on the basis of formulas derived form the initial equations (1) and (2):

2 2 2

z y

x

n n

n arctan

+

=

2 2 2

z x

y

n n

n arctan

con-Since the range of the employed arc functions is 〈-90°; 90°〉, and the uring range of the sensor equals 〈-180°; 180°〉, the last step is to find val-ues of the measured tilt angles over the full angular range by the way of

meas-checking the sign of the component acceleration g z, represented by the variable m z Both for the pitch and the roll, three cases are possible:

2

2 3

2

2 3

180 0

, 0

180 0

, 0 0

α α

α

α α

α

α α

z z z

m m

2

2 3

2

2 3

180 0

, 0

180 0

, 0 0

β β

β

β β

β

β β

z z z

m m

constant value of the related sensitivity is ensured over the whole urement range [2] The algorithm can be realized in the following steps:

meas-1 Input of the calibration data: a x , a y , a z , b x , b y , b z, ∆U

2 Readout of the indications of the sensor: U x , U y , U z

3 Determination of the variables m x zin accordance with (6)

4 Verification of the condition (8)

5 Determining the variables n x zin accordance with (9)

6 Initial calculation of the pitch and the roll according to (10) – (11)

7 Determination of the pitch and the roll according to (12) – (13)

Experimental studies, performed on a tilt sensor built of two dual-axis celerometers ADXL 202E by Analog Devices, have proven correctness of the algorithm and yielded a relatively high accuracy of the sensor, as far as MEMS devices are concerned Assuming that it may be evaluated by the maximal value of the difference between the value of the roll angle applied

ac-by means of the used test station and the value determined with respect to the average of respective indications of the sensor, the accuracy was found out to be of 0.18° (0.05 % as referred to the measuring range)

Theoretical and Constructive Aspects Regarding Small Dimension Parts Manufacturing by

a subassembly of a µSPL installation

There are given different geometric patterns, as preliminary test, generated

by using a program in LabView to command the servomotors that act the x-y stage There are given, also, the results of the authors as regards the

2 ½ D configured parts by using the standard photoresist technology, ing from the idea to combine SPL with thick resist UV lithography

start-1 Introduction

Stereophotolithography utilizes the principle of successive superposition of plane-profiled layers, obtained by selective polymerization of a synthetic resin under the action of a laser emitting ultraviolet or ultraviolet-near-visible radiations

Applying of this technology in the microfabrication field requires a worthy improvement of the spatial resolution In the same time, this ap-proach proves itself very attractive, presenting a number of advantages over other micromanufacturing processes [1, 2]:

note-• direct obtaining of three-dimension objects;

• possibility to obtain complex shaped objects in a versatile manner, without using of masks, starting from the numerical coordinates of the objects, generated by a compatible CAD system;

• obtaining of micro-moulds for forming by micro-galvanizing (if a conducting support/substrate is used)

2 Description of the experimental setup and obtained results

For the time being, the research team has performed the designing, tion and execution of a device – stage with displacements on x and y direc-tions, controlled by PC, by means of a controller and a versatile interface for the motion controlling The device is designed to be a subassembly of a µSPL installation [3], being placed on the supporting plate of a UV laser

simula-In fig 1 and 2, there are presented the kinematic scheme and the 3D model, in Solid Works, of this device The experimental setup building is shown in fig 3

Fig 1 Kinematic scheme of the x-y table:1 - PC; 2 - controller; 3 - motion control interface; 4 - d.c servo-amplifier; 5 - servomotor with incorporated planetary gearing and encoder; 6 - coupler; 7 - screw and nut mechanism; 8 - course limit- ers; 9, 9’ - x, y tables; 10, 10’ - springs; 11 - laser; 12 - beam splitter; 13 - mirrors;

14 - objective; 15 - laser beam

1 2 3

8

4 5 6 7

9’ 10

11 12 1

14 15

9 10

517 Theoretical and constructive aspects regarding small dimension parts manufacturing 

Fig 2 3D model, in Solid Works, of

the x-y stage

Fig 3 Measurement of the position errors

on y direction

A laser emitting in the visible field will be used for the UV laser lining-up,

as well as for the resin thickness control

The maximum course on x-y directions is 25 mm, with a displacement

in-crement (the resolution, R) of 74 nm, as results from the relationship given

p

where: p s - the pitch of micrometer screw (0.5 mm), i g – the transmission

ratio of planetary gearing (3375/64), ∆ϕ - the encoder increment (2π/128

rad)

a x direction b y direction Fig 4 Normal (Gaussian) distributions for 50 measurements, representing the

displacement errors on x and y directions

518 L. Bogatu, D. Besnea, N. Alexandrescu, G. Ionascu, D. Bacescu, H. Panaitopol

By initiating of commands of the stage in different positions on x-y tions with return in a reference position and, then, by displacing the two (x-y) tables successively, with a same number of steps, the positioning er-ror and the repeatability error were determined Thus, the influence of the errors of elements from the kinematic chains of motion transmission was established An inductive transducer connected by an electronic interface

direc-to PC was used for measurements More measurements (50 tions) were performed and the Gauss distribution curves were drawn, fig 4 Based on the experimental results (table 1), a positioning error of

determina-± 5 µm and a repeatability error of 10 µm can be estimated

Table 1: Experimental results

Fig 5 Patterns generated and drawn based on the program in LabView

In the following fig 6 and 7 are shown examples of 2 ½ D parts obtained

by using standard photolithography (UV) processes for configuration The covered technological stages are: base preparing, photoresist layer deposi-tion (solid photoresist applied by lamination, for the parts shown in fig 6 and, respectively, liquid photoresist deposited by spinning for the struc-tures presented in fig 7), UV-rays exposure, selective galvanic deposition (in the gaps of the photoresist mask), photoresist removing and releasing

of the parts from the deposition support

519 Theoretical and constructive aspects regarding small dimension parts manufacturing 

Fig 6 Armature core disk and relay lamella:

permalloy (thick 0.13 mm); copper (thick

at one value, for example the uniform thickness of the deposited (grown) layer, as is in our applications This paper introduces an experimental setup, which consists, for the time being, of a x-y stage controlled by PC, with nanometer resolution, and that is designed to be a subassembly of a µSPL installation The information offered by the structure 3D model will

be transposed by means of a post processor in a standard programming language that commands the displacement on the x-y-z coordinate axes by

a controller and a motion interface These are the research development directions of the working team, in the future

References

[1] H Yu, B Li, X Zhang, Sensors and Actuators A 125 (2006) 553 [2] G Ionascu ”Technologies of Microtechnics for MEMS” (in Roma-nian), Cartea Universitara Publishing House, Bucharest, 2004

[3] L Bogatu, D Besnea, N Alexandrescu, G Ionascu, D Bacescu, H Panaitopol, Acta Technica Napocensis, Series: Applied Mathematics and Mechanics 49, vol III, Cluj-Napoca, Romania (2006) 727

520 L. Bogatu, D. Besnea, N. Alexandrescu, G. Ionascu, D. Bacescu, H. Panaitopol

Comparative Studies of Advantages of Integrated Monolithic versus Hybrid Microsystems

M Pustan, Z Rymuza

Warsaw University of Technology

Institute of Micromechanics and Photonics,

ul Sw.A.Boboli 8, Warsaw, 02-525, Poland

Abstract

This paper shows a comparative study of differences between monolithic microsystems and hybrid microsystems The manufacturing technologies, the performance, and financial aspects are the main criteria which were taken into consideration in this study The establishment of the manufac-turing cost of monolithic versus hybrid microsystems was carried out, re-spectively In this way collaborations with over 50 manufacturing compa-nies had been performed for estimation of manufacturing cost of mono-lithic microsystems versus hybrid microsystems

1 Introduction

A microsystem is defined as an intelligent miniaturized system comprising sensing, processing and/or actuating functions These would normally combine two or more of the following: electrical, mechanical, optical, chemical, biological magnetic or other properties integrated onto a single chip or a multichip hybrid

The microsystem can carry out four basic functions: (a) perception of the environment with a sensor; (b) signal processing, data analysis and de-cision-making, with a microelectronic circuit; (c) reaction upon environ-mental input according to data received, with an actuator; (d) communica-tion with the outside world, with signal receivers or generators

Microsystems meet the growing demand of the market for systems that are increasingly reliable, multifunctional, miniaturized, cheap, possibly self-managed and/ or programmable As previously indicated, two main requirements account for the evolution towards system miniaturization:

• Manufacturing at very low unit cost for mass application;

• Reducing the size of devices for applications aimed at very narrow spaces or requiring minimal weight

2 Monolithic and hybrid microsystem

The two constructional technologies of microengineering are tronics and micromachining Microelectronics, producing electronic cir-

microelec-cuitry on silicon chips, is a very well development technology mentary metal-oxide-semiconductor (CMOS) technology is a major class

Comple-of electronic circuit Micromachining is the name for the techniques used

to produce the structures and moving parts of microengineered devices

Fig 1 Classification of micromachining for monolithic and hybrid microsystems

The various microsystems technologies (MST) can be classified as shown

in the Figure 1 The diversity of microsystem technologies is a result of the wide range of materials that can be used and the number of different form-ing or machining techniques Materials used are silicon, quartz, ceramics, metals, plastics, glass, piezoelectric layers, etc

The passive microcomponents cannot realize signal

transforma-tion, information processing or system control This category includes ters, resistors, capacitors, inductors, transformers and diodes The active microcomponents can detect, process, transform and evaluate external sig-

fil-Microsystem

Technology

ActiveMicrosystems

PassiveComponents

Hybrid Microsystems

2D Multichip

3D Structure

Anodicbonded

Flip chip

Monolithic Microsystems

Surface MicromachinedBulkMicromachined Combination Micromachining(Bulk+Surface)

nals, can make decision based on the obtained information and finally can convert the decision into corresponding actuator commands

In many cases, mechanical structures are combined with active electronic circuitry There are two major techniques employed, monolithic and hybrid Microsystems may be constructed from parts produced using different technologies on different substrates, connected together, i.e a hybrid microsystem (Fig.2a) Alternatively, all components of a system could be constructed on single substrate, i.e a monolithic microsystem (Fig.2b)

Fig.2 Hybrid approach (a) versus monolithic integration (b) of MEMS and CMOS

The decision to merge CMOS and Microelectromechanical Systems (MEMS) devices to realize a given product is mainly driven by perform-ance and cost On the performance side, co-fabrication of MEMS struc-tures with drive/sense capabilities with control electronics is advantageous

to reduce parasitic, device power consumption, noise levels as well as packaging complexities, yielding to improved system performance [1-3] With MEMS and electronic circuits on separate chips (Fig.3) the parasitic capacitance and resistance of interconnects, bond pads, and bond wires can attenuate the signal and contribute significant noise

Fig 3 Accelerometer showing control IC on the left and sensing cell on

the right (Freescale Semiconductor, Inc.)

On the economic side, an improvement in system performance of the grated MEMS device would result in an increase in device yield and den-sity, which ultimately translates into a reduction of the chip’s cost More-over, eliminating wire bonds to interconnect MEMS and integrated circuits (IC) could potentially result in reduced packaging complexities which will eventually lead to more reliable systems, and to lower manufacturing cost Modular integration will allow the separation of development and optimi-zation of electronics and MEMS processes There are three main integra-

MEMS

523 Comparative studies of advantages of integrated monolithic versus hybrid