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Simulation of a humidity-sensitive double-layer system
Sensors
and
Actuators
B,
18-19
(1994)
303
303-307
Simulation of a humidity-sensitive double-layer system Gerald Gerlach”, Karsten Sagerb and Andreas Schrothb %.dim D-01062
of precision Mechamkv, Dresden {Gemzany)
%stilute~of
Technical
Acoustics,
Dresden
Unkersi~
of Technology,
hfcnnmens~~t?
13,
Abstract Humidity-dependent swelling of polyimide layers on silicon membranes is described. A simulation strategy using the iinite element method (FEM) to predict the resultant deformation of the double-layer system is obtained. A humidity extension coefficient a, is introduced and determined by means of X-ray bending measurement and backward simulation. The FEN is used to investigate the influence of possible technological tolerances of layer thickness, coefficient LY,and chip-clamping on the behaviour of the system. For convenience an analytical equation for temperature- or humidity-induced deformation of bimorphs is presented, using the concentrated-element theory. Finally, a comparison of the results simulated by FEM shows a satisfactory agreement with experimental investigations.
Introduction In connection with general investigations of conventional and new passivation layers the behaviour of different passivation materials under the influence of humidity was studied. By using polyimide layers a significant expansion effect dependent on the relative humidity of the ambient air was observed. This paper discusses the basic effect, its possible influences on sensor behaviour and performance, and possible uses for the design of humidity sensors. To answer these questions a strategy for modelling the observed behaviour had to be developed. Finite element modelling (FEM), as a standard numerical modelling technique for predicting sensor behaviour, is preferred.
by bending of the double-layer system formed by basic silicon and the polyimide layer. The bimorph-like behaviour is based on the humidity-induced volume expansion of the polyimide material used in connection with the nearly non-expanding basic silicon. The amount of water which can be absorbed depends on the level of saturation of the polyimide used. Theoretically calculated values of 16 mass% water are not reached in reality. Measuredvalues at a relative humidity (r-h.) of 100% are 1.5 to 6% water [l], whereas affinity to water of polyimide merely depends on the annealing level of the polyimide [2]. It can be assumed that humidity-induced volume extension of polyimide is relatively linear and can be compared with volume extension caused by temperature changes.
Effects caused by humidity Polyimide materials are known to be sensitive to humidity changes in surrounding media because of their ability to absorb water. Mostly changes in electrical properties, like conductivity and dielectric&y, are considered and used. The chemical bonding of hydrogen and OH- molecules at unsaturated bonds of the polyimide chain causes a volume expansion of the material and therefore changes in its mechanical properties and behaviour. The change of the output voltage of piezoresistors, which are implanted in the transducer membrane, rep resents a change of mechanical stress at the location of the resistors on the diaphragm. This change is caused
0925-KM5/94/$~7.00 8 1994 Elsevier Sequoia. SSDI 09254qO5(93)01214-0
All rights reserved
Determination of humidity-induced volume extension of polyimide The obtained similarity of the behaviour of a humidityinfluenced double-layer system to the behaviour of temperature biiorph systems allows us to use simulation methods and tools developed for temperature-induced volume extension. Especially programs based on the finite element method (FEM) promise efficient use. Therefore, relative humidity is considered analogous to temperature and the temperature coefficient a will be replaced by the humidity-fraction coefficient (Ye A value for a9 was given in ref. 1 with 2.2 x 1O-5/% r.h. To determine the value of aV, polyimide layers
with thicknesses between 0.7 and 4 pm were deposited on a number of unstructured 3 inch silicon wafers. Later these wafers were loaded with several humidity levels. The bending of the double-layer system was measured by means of X-ray curvature measurements, The geometry of the layered wafer was described by a FEM model and bending of the system was simulated using the temperature extension capability of the FEM program. The simulated curves of bending versus humidity for different coefficients aq were compared with measured curves. By means of inverse simulation a+, could be determined in a range between 4.5 X 10e5 and 8.5 X 1O-5/% r.h. Differences are supposed to be caused by different annealing times and temperatures. Due to the limited number of experimental results a significant correlation between annealing parameters and the value of a9 could not be found. An average coefficient cc,=6.5 x 10m5/% r.h. was assumed for the following simulations.
Simulation results As already mentioned, the relation between relative humidity and induced bending mostly depends on concrete fabrication history of the polyimide used. To investigate the influence of technological tolerances on the sensor behaviour various FE simulations were carried out. The geometry of the pressure sensor as an example of piezoresistive sensors was developed as a FE model (Fig. l), where the silicon transducer membrane with a thickness of about 10 pm thick was clamped by the silicon bulk material. A thin polyimide layer of about 2 pm was deposited on the membrane. Other rinner layers were neglected.
Deformation of this geometry at relative humidity values between 10 and 90% was described by the value of induced mechanical stress in the middle of the membrane. This model was varied in thickness of the polyimide layer, clamping conditions and humidity coefficient a, Results for thickness variation are shown in Fig. 2. It can be seen that thickness tolerances of 0.5 pm would cause changes in mechanical stress of about 0.1~105 Pa/% r.h. A tolerance of the coefficient a, shows a similar influence (Fig. 3). Increase of its value by 1 X 10W5/% r.h. results in an increase of induced stress of about 0.6X104 Pa/% r.h. In this way, conclusions about the reliability of simulation or the value of a9 can be obtained if thicknesses of the polyimide layer and the silicon membrane are known. The clamping condition of the whole sensor chip, referring to different packaging technologies (Fig. 4), is very important not only for the value of induced stress but also for its character. The freely movable complete chip without any direct clamping, like the measured samples, shows about a 70% higher output than chips which are clamped at the bottom of the bulk (as, for instance, glass-bonded packaging demands). Neglecting clamping, as assumed in most of the analytical calculations, the simple membrane shows negative stress values. This means compressive instead of tensile stress at the detected location. The differences are clearly caused by membrane stress induced by deformation of the silicon bulk which are superposed on the basic bending stress. Though the bulk is comparatively thick
‘.0Etoo7 r , I’ 8.OEt006
x
i PI = 15/m -----,P, I 2 ----,R - 2.5$ --- tPI-5 pm l----l-
.c6.OEtO06
I’ I ,
/ I’
:
0 e % :4.OEt006 2 n .c 20Et006
O.OE+OOD
Fig. 1. Finite element model of a polyimide-layered silicon membrane. Due to symmetry only a quarter of the whole structure is considered.
a
20
‘
Fig. 2. Induced mechanical stress as a function of relative humidity with various polyimide-layer thicknesses (@‘I), silicon-membrane thickness (tS1) of 10 pm, no clamping and a humidity coefficient + of 6.5 X lO-‘/% rh.
1 .OEt006
“1 O.OE+OOO 0
20 relative
40 humidity
60 in sr.h.
80
100
Fig. 3. Induced mechanical stress as a function of relative humidity with various humidity coefficients CT.,polyimidc-layer thickness (tP1) of 2 pm, silicon-membrane thickness (tS1) of 10 @rn and no clamping. 4.OE+006
3.OEt006
! 4 .c
O.OE+OOO
-l.OE+oo6
! -
Fig. 4. Induced mechanical stress as a function of relative humidity with various types of clamping, potyimide-layer thickness (tP1) of 2 pm, silicon-membrane thickrress (tS1) of 10 pm and a humidity coefficient 5 of 6.5 x lo-‘/% r.h.
I,
i I
Fig. 5. Obtaining an analytical equation for deflection-induced mechanical stress in layered systems by means of nehvork-theoreticat theories.
With the assumption that long rectangular plates (with a length-to-height relation > 3) can be described as twodimensional beams [3], the network-theoretical description of a bending beam can be applied. This model, which is based on concentrated elements, will be extended with additional elements describing the deformation-causing fraction force as a controlled source element. Mean material constants are used to represent the double-layer character [4]. The clamping is partly included by means of a geometry-dependent rotational spring [5] (Fig. 5). Using this theory a comparatively simple equation representing deformation and mechanical stresses of a temperature- or humidity-deformed double-layer system was derived [4]:
A4, h, and bI are induced stress, where 0, k, &obirniti, geometrical coefficient for clamping spring (0.75 for the mentioned geometry [5]), Young’s modulus of polyhnide, relative humidity in %, thickness and length of the polyimide layer, respectively.
it will be deformed by the polyimide layer in a packagingdependent way. Experimental and discussion Analytical description method Because of difficulties of the generalization of results of common l?EM program systems the deduction of a simple analytical description of humidity-induced deformation of double-layer systems seemed to be useful.
To prove the reliability of the assumed coefficients and simulation results the measured relation between mechanical stress and relative humidity was simulated by means of the above-mentioned FE model and the obtained analytical eqn. (1) for a relative humidity range N-90%. The minimum value used for a+, of
20
40
60
80
relative humidity in %RH
Fig. 6. Induced mechanical stress as a function of relative humidity, comparing FE-simulated measured (c) curves. The silicon chip is completely covered with the polyimide layer.
(a), analytically calculated (b) and
a. 10~ $ .a : 6. IO6 0 2 rl 6
; 4. 10 .rl nc c Y & 2. lo6
relative humidity in %RH
Fig. 7. Induced mechanical stress as a function of relative humidity, comparing FE-simulated (a) analytically calculated (b) and measured curves (c). Only half of the silicon membrane is covered with polyimide.
4.5~10-~/% r.h. is due to the fabrication history of the measured samples. The results are presented in Fig. 6 and show a good correspondence between simulated and measured values. The analytically calculated curve runs at much smaller values. Further FE simulations showed that these analytically calculated values exactly represent a membrane bending without consideration of bulk deformation. Therefore, analytical approximation is shown to be useful in cases of noncovered clamping. A small nonlinearity of the measured curve cannot be obtained reliably enough to allow further conclusions and will be neglected.
Conclusions The general behaviour of humidity-dependent swelling of thin polyimide layers can be used to develop the concept of a new type of humidity sensor. Because the geometry and technology of this sensor are based on already existing samples of a pressure sensor, it might be produced efficiently. Using the presented simulation strategy both performance and humidity sensitivity of the object could be increased by a special structure of the polyimide layer. Simultaneously, the influence of sensor clamping could be decreased re-
307
markably [6]. In Fig. 7, by means of analytical and FE simulation, predicted curves for the humidity dependence of the stresses are compared with measured results obtained from first samples. A good correspondence is seen. Due to the fact that the FE simulation shows a higher sensitivity than the measured results, an extension coefficient CZ~a little smaller than the value of 6.5X lo-‘/% r.h., which was assumed for thii sample’s fabrication, could be concluded.
References
G.A. Bernier and D.E. Kline, Dynamic mechanical behaviour of a polyimide, 1. Appl. P&m. Sci., 12 (1968) 59Z-604. C.J. Wolf, D.L. Fanter and R.S.Soloman, Environmental degradation of aromatic polyimide-insulated electrical wire, IEEE Tmns. Electr. InsuL, EI-19 (1984) 265-272. U. Menzel and W. Winkler, Sparmungsfelder in unendlichen Rechteckplatten, Fekgetitetechnik, 31 (1982) 248-250. G. Gerlach and M. Meyer, Zum Einfluss der AluminiumLeitbahnen auf das Temperatutverhaken integrierter piezoresistiver Drucksensoren, Rep. ITA 09/Z5/88, Dresden University of Technology, Institute of Technical Acoustics, 1988. G. Gerlach, P. Pert& and A. Schroth, The influence of clamping on sensor characteristics, paper presented at Eumsensors WI, Budapest, Hungry, Sept. 26-29, 1993. G. Gerlach, K. Sager, H. Schmidt and A. Schroth, A humidity sensor of a new type, Sensors and Actuators, (1993).
Biographies Andteas Schroth received his diploma in precision mechanics from the Chemnitz University of Technology in 1992. Since 1993 he has been a graduate student at Dresden University of Technology. His current research interests are in the areas of sensor and actuator modelling, especially in sensor design and simulation in the field of microsystem technologies and precision mechanics. Karsten Sager received his diploma in information technology from Dresden University of Technology in 1989. Afterwards he became a scientific assistant at the Institute of Acoustics of the same university. Since then he has been working on the analysis and synthesis of electromechanical systems. A certain area of his research is the design and simulation of micromechanical systems (e.g., pressure and humidity sensors). Gerald Gerlachreceived his diploma and his Dr.-Ing. degree in information technology from Dresden University of Technology in 1983 and 1987, respectively. From 1983 to 1992 he worked in R&D in several measuring instrument companies. He has developed design methods and simulation tools for silicon pressure sensors. In 1993 he became a professor for precision mechanics technology at Dresden University of Technology. His current research interests are in the areas of sensor and actuator modelling, design, simulation and technology in the field of precision mechanics and micromechanics.
and
Actuators
B,
18-19
(1994)
303
303-307
Simulation of a humidity-sensitive double-layer system Gerald Gerlach”, Karsten Sagerb and Andreas Schrothb %.dim D-01062
of precision Mechamkv, Dresden {Gemzany)
%stilute~of
Technical
Acoustics,
Dresden
Unkersi~
of Technology,
hfcnnmens~~t?
13,
Abstract Humidity-dependent swelling of polyimide layers on silicon membranes is described. A simulation strategy using the iinite element method (FEM) to predict the resultant deformation of the double-layer system is obtained. A humidity extension coefficient a, is introduced and determined by means of X-ray bending measurement and backward simulation. The FEN is used to investigate the influence of possible technological tolerances of layer thickness, coefficient LY,and chip-clamping on the behaviour of the system. For convenience an analytical equation for temperature- or humidity-induced deformation of bimorphs is presented, using the concentrated-element theory. Finally, a comparison of the results simulated by FEM shows a satisfactory agreement with experimental investigations.
Introduction In connection with general investigations of conventional and new passivation layers the behaviour of different passivation materials under the influence of humidity was studied. By using polyimide layers a significant expansion effect dependent on the relative humidity of the ambient air was observed. This paper discusses the basic effect, its possible influences on sensor behaviour and performance, and possible uses for the design of humidity sensors. To answer these questions a strategy for modelling the observed behaviour had to be developed. Finite element modelling (FEM), as a standard numerical modelling technique for predicting sensor behaviour, is preferred.
by bending of the double-layer system formed by basic silicon and the polyimide layer. The bimorph-like behaviour is based on the humidity-induced volume expansion of the polyimide material used in connection with the nearly non-expanding basic silicon. The amount of water which can be absorbed depends on the level of saturation of the polyimide used. Theoretically calculated values of 16 mass% water are not reached in reality. Measuredvalues at a relative humidity (r-h.) of 100% are 1.5 to 6% water [l], whereas affinity to water of polyimide merely depends on the annealing level of the polyimide [2]. It can be assumed that humidity-induced volume extension of polyimide is relatively linear and can be compared with volume extension caused by temperature changes.
Effects caused by humidity Polyimide materials are known to be sensitive to humidity changes in surrounding media because of their ability to absorb water. Mostly changes in electrical properties, like conductivity and dielectric&y, are considered and used. The chemical bonding of hydrogen and OH- molecules at unsaturated bonds of the polyimide chain causes a volume expansion of the material and therefore changes in its mechanical properties and behaviour. The change of the output voltage of piezoresistors, which are implanted in the transducer membrane, rep resents a change of mechanical stress at the location of the resistors on the diaphragm. This change is caused
0925-KM5/94/$~7.00 8 1994 Elsevier Sequoia. SSDI 09254qO5(93)01214-0
All rights reserved
Determination of humidity-induced volume extension of polyimide The obtained similarity of the behaviour of a humidityinfluenced double-layer system to the behaviour of temperature biiorph systems allows us to use simulation methods and tools developed for temperature-induced volume extension. Especially programs based on the finite element method (FEM) promise efficient use. Therefore, relative humidity is considered analogous to temperature and the temperature coefficient a will be replaced by the humidity-fraction coefficient (Ye A value for a9 was given in ref. 1 with 2.2 x 1O-5/% r.h. To determine the value of aV, polyimide layers
with thicknesses between 0.7 and 4 pm were deposited on a number of unstructured 3 inch silicon wafers. Later these wafers were loaded with several humidity levels. The bending of the double-layer system was measured by means of X-ray curvature measurements, The geometry of the layered wafer was described by a FEM model and bending of the system was simulated using the temperature extension capability of the FEM program. The simulated curves of bending versus humidity for different coefficients aq were compared with measured curves. By means of inverse simulation a+, could be determined in a range between 4.5 X 10e5 and 8.5 X 1O-5/% r.h. Differences are supposed to be caused by different annealing times and temperatures. Due to the limited number of experimental results a significant correlation between annealing parameters and the value of a9 could not be found. An average coefficient cc,=6.5 x 10m5/% r.h. was assumed for the following simulations.
Simulation results As already mentioned, the relation between relative humidity and induced bending mostly depends on concrete fabrication history of the polyimide used. To investigate the influence of technological tolerances on the sensor behaviour various FE simulations were carried out. The geometry of the pressure sensor as an example of piezoresistive sensors was developed as a FE model (Fig. l), where the silicon transducer membrane with a thickness of about 10 pm thick was clamped by the silicon bulk material. A thin polyimide layer of about 2 pm was deposited on the membrane. Other rinner layers were neglected.
Deformation of this geometry at relative humidity values between 10 and 90% was described by the value of induced mechanical stress in the middle of the membrane. This model was varied in thickness of the polyimide layer, clamping conditions and humidity coefficient a, Results for thickness variation are shown in Fig. 2. It can be seen that thickness tolerances of 0.5 pm would cause changes in mechanical stress of about 0.1~105 Pa/% r.h. A tolerance of the coefficient a, shows a similar influence (Fig. 3). Increase of its value by 1 X 10W5/% r.h. results in an increase of induced stress of about 0.6X104 Pa/% r.h. In this way, conclusions about the reliability of simulation or the value of a9 can be obtained if thicknesses of the polyimide layer and the silicon membrane are known. The clamping condition of the whole sensor chip, referring to different packaging technologies (Fig. 4), is very important not only for the value of induced stress but also for its character. The freely movable complete chip without any direct clamping, like the measured samples, shows about a 70% higher output than chips which are clamped at the bottom of the bulk (as, for instance, glass-bonded packaging demands). Neglecting clamping, as assumed in most of the analytical calculations, the simple membrane shows negative stress values. This means compressive instead of tensile stress at the detected location. The differences are clearly caused by membrane stress induced by deformation of the silicon bulk which are superposed on the basic bending stress. Though the bulk is comparatively thick
‘.0Etoo7 r , I’ 8.OEt006
x
i PI = 15/m -----,P, I 2 ----,R - 2.5$ --- tPI-5 pm l----l-
.c6.OEtO06
I’ I ,
/ I’
:
0 e % :4.OEt006 2 n .c 20Et006
O.OE+OOD
Fig. 1. Finite element model of a polyimide-layered silicon membrane. Due to symmetry only a quarter of the whole structure is considered.
a
20
‘
Fig. 2. Induced mechanical stress as a function of relative humidity with various polyimide-layer thicknesses (@‘I), silicon-membrane thickness (tS1) of 10 pm, no clamping and a humidity coefficient + of 6.5 X lO-‘/% rh.
1 .OEt006
“1 O.OE+OOO 0
20 relative
40 humidity
60 in sr.h.
80
100
Fig. 3. Induced mechanical stress as a function of relative humidity with various humidity coefficients CT.,polyimidc-layer thickness (tP1) of 2 pm, silicon-membrane thickness (tS1) of 10 @rn and no clamping. 4.OE+006
3.OEt006
! 4 .c
O.OE+OOO
-l.OE+oo6
! -
Fig. 4. Induced mechanical stress as a function of relative humidity with various types of clamping, potyimide-layer thickness (tP1) of 2 pm, silicon-membrane thickrress (tS1) of 10 pm and a humidity coefficient 5 of 6.5 x lo-‘/% r.h.
I,
i I
Fig. 5. Obtaining an analytical equation for deflection-induced mechanical stress in layered systems by means of nehvork-theoreticat theories.
With the assumption that long rectangular plates (with a length-to-height relation > 3) can be described as twodimensional beams [3], the network-theoretical description of a bending beam can be applied. This model, which is based on concentrated elements, will be extended with additional elements describing the deformation-causing fraction force as a controlled source element. Mean material constants are used to represent the double-layer character [4]. The clamping is partly included by means of a geometry-dependent rotational spring [5] (Fig. 5). Using this theory a comparatively simple equation representing deformation and mechanical stresses of a temperature- or humidity-deformed double-layer system was derived [4]:
A4, h, and bI are induced stress, where 0, k, &obirniti, geometrical coefficient for clamping spring (0.75 for the mentioned geometry [5]), Young’s modulus of polyhnide, relative humidity in %, thickness and length of the polyimide layer, respectively.
it will be deformed by the polyimide layer in a packagingdependent way. Experimental and discussion Analytical description method Because of difficulties of the generalization of results of common l?EM program systems the deduction of a simple analytical description of humidity-induced deformation of double-layer systems seemed to be useful.
To prove the reliability of the assumed coefficients and simulation results the measured relation between mechanical stress and relative humidity was simulated by means of the above-mentioned FE model and the obtained analytical eqn. (1) for a relative humidity range N-90%. The minimum value used for a+, of
20
40
60
80
relative humidity in %RH
Fig. 6. Induced mechanical stress as a function of relative humidity, comparing FE-simulated measured (c) curves. The silicon chip is completely covered with the polyimide layer.
(a), analytically calculated (b) and
a. 10~ $ .a : 6. IO6 0 2 rl 6
; 4. 10 .rl nc c Y & 2. lo6
relative humidity in %RH
Fig. 7. Induced mechanical stress as a function of relative humidity, comparing FE-simulated (a) analytically calculated (b) and measured curves (c). Only half of the silicon membrane is covered with polyimide.
4.5~10-~/% r.h. is due to the fabrication history of the measured samples. The results are presented in Fig. 6 and show a good correspondence between simulated and measured values. The analytically calculated curve runs at much smaller values. Further FE simulations showed that these analytically calculated values exactly represent a membrane bending without consideration of bulk deformation. Therefore, analytical approximation is shown to be useful in cases of noncovered clamping. A small nonlinearity of the measured curve cannot be obtained reliably enough to allow further conclusions and will be neglected.
Conclusions The general behaviour of humidity-dependent swelling of thin polyimide layers can be used to develop the concept of a new type of humidity sensor. Because the geometry and technology of this sensor are based on already existing samples of a pressure sensor, it might be produced efficiently. Using the presented simulation strategy both performance and humidity sensitivity of the object could be increased by a special structure of the polyimide layer. Simultaneously, the influence of sensor clamping could be decreased re-
307
markably [6]. In Fig. 7, by means of analytical and FE simulation, predicted curves for the humidity dependence of the stresses are compared with measured results obtained from first samples. A good correspondence is seen. Due to the fact that the FE simulation shows a higher sensitivity than the measured results, an extension coefficient CZ~a little smaller than the value of 6.5X lo-‘/% r.h., which was assumed for thii sample’s fabrication, could be concluded.
References
G.A. Bernier and D.E. Kline, Dynamic mechanical behaviour of a polyimide, 1. Appl. P&m. Sci., 12 (1968) 59Z-604. C.J. Wolf, D.L. Fanter and R.S.Soloman, Environmental degradation of aromatic polyimide-insulated electrical wire, IEEE Tmns. Electr. InsuL, EI-19 (1984) 265-272. U. Menzel and W. Winkler, Sparmungsfelder in unendlichen Rechteckplatten, Fekgetitetechnik, 31 (1982) 248-250. G. Gerlach and M. Meyer, Zum Einfluss der AluminiumLeitbahnen auf das Temperatutverhaken integrierter piezoresistiver Drucksensoren, Rep. ITA 09/Z5/88, Dresden University of Technology, Institute of Technical Acoustics, 1988. G. Gerlach, P. Pert& and A. Schroth, The influence of clamping on sensor characteristics, paper presented at Eumsensors WI, Budapest, Hungry, Sept. 26-29, 1993. G. Gerlach, K. Sager, H. Schmidt and A. Schroth, A humidity sensor of a new type, Sensors and Actuators, (1993).
Biographies Andteas Schroth received his diploma in precision mechanics from the Chemnitz University of Technology in 1992. Since 1993 he has been a graduate student at Dresden University of Technology. His current research interests are in the areas of sensor and actuator modelling, especially in sensor design and simulation in the field of microsystem technologies and precision mechanics. Karsten Sager received his diploma in information technology from Dresden University of Technology in 1989. Afterwards he became a scientific assistant at the Institute of Acoustics of the same university. Since then he has been working on the analysis and synthesis of electromechanical systems. A certain area of his research is the design and simulation of micromechanical systems (e.g., pressure and humidity sensors). Gerald Gerlachreceived his diploma and his Dr.-Ing. degree in information technology from Dresden University of Technology in 1983 and 1987, respectively. From 1983 to 1992 he worked in R&D in several measuring instrument companies. He has developed design methods and simulation tools for silicon pressure sensors. In 1993 he became a professor for precision mechanics technology at Dresden University of Technology. His current research interests are in the areas of sensor and actuator modelling, design, simulation and technology in the field of precision mechanics and micromechanics.