- Email: [email protected]
Microelectronic skin electrode
Sensors and Actuators, Bf (1990) 491-494
491
Microelectronic Skin Electrode F. Z. PADMADINATA,
J. J. VEERHOEK, G. J. A. VAN DIJK and J. H. HUIJSING
Faculty of Electrical Enginee+ng, Deut University of Technology, Del/t (The Nether&n&)
Abstract
A microelectronic skin electrode in a standard bipolar process has been fabricated for ECG measurements. A buffer-amplifier and two bond gaps provided for contact with the supply voltage and the output signal are integrated on a silicon chip. No paste is required in applying this electrode to the skin. The substrate of the chip is designed to function as the input of the amplifier and as the sensitive part which detects biopotentials from the skin. The substrate is covered by a metal disc to protect it from body fluid contamination during measurement. The metal is attached to the substrate by a conductive adhesive. Stainless steel and silver foil electrodes have been used for the experiments. Packaging has been done by using silicone rubber and epoxy resin. Some characteristic measurements are given, and some ECG measurements are shown.
dance buffer-amplifier must be provided at the electrode site. A low output impedance of the buffer-amplifier is needed for the reduction of electrical interferences. We call this type of skin electrode an active dry skin electrode. Figures 1 and 2 consecutively show the influence of a power line on ECG measurement, the first using wet skin electrodes and the second using active dry skin electrodes. A common signal coming from the Power
line
Instrument E.C.G.
Introduction
The majority of skin electrodes are metal plates placed on the skin after degreasing and the application of an electrolyte in the form of an electrode paste or jelly. This is necessary to establish and maintain a good contact between skin and electrode. We classify such electrodes as wet electrodes. There are some disadvantages to applying wet electrodes, such as: they are time consuming, irritating, and unsuitable for using long-term monitoring because the paste dries out after a passage of time. Besides, the lead wires between the electrode and the amplifier are susceptible to electrical interference and the result is some artifacts on the detecting signal (Fig. 1). To overcome such problems, several researchers, Bergey et al. [I], Richardson [2], Lopez and Richardson [3] and Ko and Hynecek [4], developed a new type of skin electrodes. The new type of electrodes does not require any paste when applied to the skin, and they are classified by the name of dry electrodes. To adapt to the higher resistance which occurs between the skin and the electrode as compared to a wet electrode, a self-contained high input impe-
Fig. 1. ECG measurement using wet electrodes.
Power ----------
line
iv-
Fig. 2. ECG measurement using active dry electrodes. 0
Elsevier Sequoia/Printed
in The Netherlands
492
494
with the other experiments. A typical result is given in Fig. 9, using stainless steel and silver foil electrodes.
Conehsions
It has been shown that it is possible to make an active dry skin electrode in a standard bipolar process. Motion artifacts are still dominant in the measurement of ECG and can be reduced by higher input impedance and lower input bias current [5]. The noise of the device can be reduced by using a metal layer evaporated on the substrate, as shown by noise performances for the silver layer in Fig. 8. Another version of this new type of active dry skin electrode with P-channel JFETs (junction FETs) is under development. The input impedance of this version will be larger and the input bias current will be smaller, which gives a reduction in the motion artifact effects.
Ackaow
b
The authors wish to acknowledge the process development by the members of DIMES (Dr P. Sarro, Dr L. Nanver, A. Bouwman, R. Maley and J. Groeneweg). References 1 G. E. Rergey. R. D. Squint and W. C. Sipple, Electrocardio-
2 3 4
5
gram n&ding with p&&as elect&s, IEEE Tram. Biomed. Em. BME-I8 (1971) 206. P. C. Richahon, The i&ulatLd electrode, Proc. Am Conf. Engineering in M?dicine a?ld Biology, Bomln, MA, U.S.A., 1967. A. J. Lopez and P. C. Rihudson, Capaoitive electrooardiographic and bioelectric electrodes, IEEE Trans. Biomed. Eng., BME-16 (1%9) 99. W. H. Ko and J. Hynwk, Dry electrodes and electrode amplifiers, in H. A. Miller and D. C. Harrison (ads.), Biomedical Electrode Tehcnology, Academic Press, New York, 1974, pp. 169-181. -_ P. Zipp and H. Ahrens, A model of bioelectrode motion artefact and reduction of artefaet by amplifier input stage design, J. Biomed. Eng., 1 (1979) 273-276.
493 TABLE 1. Performance skin electrode
characteristics
17 1 10 d.c. to 75 0.35 2.5 - 15 0.1 500 10 20
Input bias current Input resistance Output resistance Bandwidth Noise voltage Supply voltage Accuracy Max. load resistance Min. load resistance Supply current
-
silver-foil
---
of the microelectronic
___
silver-layer
nA Gohm ohm kHz /W/Hz V % kohm kohm PA
stainlesssteel
100
0.1’ 5
I
“’ 100
10 Frsquency
Fig. 6. Microphotograph
of a chip electrode.
Fig. 8. The noise performance
sponds to the maximum voltage variation of 0.3 mV. The Darlington input transistors, biased at a collector current I, = 0.5 PA, have an input current of about 0.2 nA. The complete circuit of the buffer-amplifier is shown in Fig. 5. The microphotograph of the chip is given in Fig. 6. Table 1 shows a typical performance of the microelectronic skin electrode. The frequency response of the microelectronic skin electrode is shown in Fig. 7. The noise performances of the
60
-
50
-20
(Hz)
of the encapsulated
encapsulation devices are shown in Fig. 8. The noise measurement has been done for three types of substrate cover, i.e. silver foil, stainless steel, and a silver layer of 300 nm. Measurements
The basic structure for the measurements is shown in Fig. 3. To reduce the EMG effects, the two electrodes were placed on the chest of the patient. In this experiment we made ECG measurements using a three-lead system. Different signals between the two microelectronic skin electrodes are detected by an instrument amplifier and are displayed by a digital memory oscilloscope. One metal electrode is applied to the right leg and behaves as common to the two other electrodes. The ECG measurements were made under normal conditions, simultaneously
‘, ,___ ‘..,
-30 -40 1
“““’ 10
-
Fig. 7. The frequency electrode.
100
“_“’ 1000 Frequency
response
“““’ 10000 [Hz1
“““d 100000
“1000000
of the microelectronic
device.
skin Fig. 9. An example
of the ECG results.
494
with the other experiments. A typical result is given in Fig. 9, using stainless steel and silver foil electrodes.
Conclusions
It has been shown that it is possible to make an active dry skin electrode in a standard bipolar process. Motion artifacts are still dominant in the measurement of ECG and can be reduced by higher input impedance and lower input bias current [5]. The noise of the device can be reduced by using a metal layer evaporated on the substrate, as shown by noise performances for the silver layer in Fig. 8. Another version of this new type of active dry skin electrode with P-channel JFETs (junction FETs) is under development. The input impedance of this version will be larger and the input bias current will be smaller, which gives a reduction in the motion artifact effects.
Acknowledgements
The authors wish to acknowledge the process development by the members of DIMES (Dr P. Sarro, Dr L. Nanver, A. Bouwman, R. Maley and J. Groeneweg).
1 G. E. Bergey, R. D. Squires and W. C. Sipple, Electrocardiogram recording with pasteless electrodes, IEEE Trans. Biomed. Eng., EME- 18 ( 197 1) 206. 2 P. C. Richardson, The insulated electrode, Proc. Ann. Conf
Engineering in Medicine and Biology, Boston, MA, U.S.A., 196% 3 A. J. Lopez and P. C. Richardson, graphic
and bioelectric
electrodes,
EME-16 (1969) 99. 4 W. H. Ko and J. Hynecek,
Capacitive
electrocardio-
IEEE Trans. Biomed. Eng.,
Dry electrodes and electrode and D. C. Harrison (eds.), Biomedical Electrode Tehcnology, Academic Press, New York, 1974, pp. 169-181. 5 P. Zipp and H. Ahrens, A model of bioelectrode motion artefact and reduction of artefact by amplifier input stage design, J. Biomed. Eng., I (1979) 273-276. amplifiers,
in H.
A.
Miller
491
Microelectronic Skin Electrode F. Z. PADMADINATA,
J. J. VEERHOEK, G. J. A. VAN DIJK and J. H. HUIJSING
Faculty of Electrical Enginee+ng, Deut University of Technology, Del/t (The Nether&n&)
Abstract
A microelectronic skin electrode in a standard bipolar process has been fabricated for ECG measurements. A buffer-amplifier and two bond gaps provided for contact with the supply voltage and the output signal are integrated on a silicon chip. No paste is required in applying this electrode to the skin. The substrate of the chip is designed to function as the input of the amplifier and as the sensitive part which detects biopotentials from the skin. The substrate is covered by a metal disc to protect it from body fluid contamination during measurement. The metal is attached to the substrate by a conductive adhesive. Stainless steel and silver foil electrodes have been used for the experiments. Packaging has been done by using silicone rubber and epoxy resin. Some characteristic measurements are given, and some ECG measurements are shown.
dance buffer-amplifier must be provided at the electrode site. A low output impedance of the buffer-amplifier is needed for the reduction of electrical interferences. We call this type of skin electrode an active dry skin electrode. Figures 1 and 2 consecutively show the influence of a power line on ECG measurement, the first using wet skin electrodes and the second using active dry skin electrodes. A common signal coming from the Power
line
Instrument E.C.G.
Introduction
The majority of skin electrodes are metal plates placed on the skin after degreasing and the application of an electrolyte in the form of an electrode paste or jelly. This is necessary to establish and maintain a good contact between skin and electrode. We classify such electrodes as wet electrodes. There are some disadvantages to applying wet electrodes, such as: they are time consuming, irritating, and unsuitable for using long-term monitoring because the paste dries out after a passage of time. Besides, the lead wires between the electrode and the amplifier are susceptible to electrical interference and the result is some artifacts on the detecting signal (Fig. 1). To overcome such problems, several researchers, Bergey et al. [I], Richardson [2], Lopez and Richardson [3] and Ko and Hynecek [4], developed a new type of skin electrodes. The new type of electrodes does not require any paste when applied to the skin, and they are classified by the name of dry electrodes. To adapt to the higher resistance which occurs between the skin and the electrode as compared to a wet electrode, a self-contained high input impe-
Fig. 1. ECG measurement using wet electrodes.
Power ----------
line
iv-
Fig. 2. ECG measurement using active dry electrodes. 0
Elsevier Sequoia/Printed
in The Netherlands
492
494
with the other experiments. A typical result is given in Fig. 9, using stainless steel and silver foil electrodes.
Conehsions
It has been shown that it is possible to make an active dry skin electrode in a standard bipolar process. Motion artifacts are still dominant in the measurement of ECG and can be reduced by higher input impedance and lower input bias current [5]. The noise of the device can be reduced by using a metal layer evaporated on the substrate, as shown by noise performances for the silver layer in Fig. 8. Another version of this new type of active dry skin electrode with P-channel JFETs (junction FETs) is under development. The input impedance of this version will be larger and the input bias current will be smaller, which gives a reduction in the motion artifact effects.
Ackaow
b
The authors wish to acknowledge the process development by the members of DIMES (Dr P. Sarro, Dr L. Nanver, A. Bouwman, R. Maley and J. Groeneweg). References 1 G. E. Rergey. R. D. Squint and W. C. Sipple, Electrocardio-
2 3 4
5
gram n&ding with p&&as elect&s, IEEE Tram. Biomed. Em. BME-I8 (1971) 206. P. C. Richahon, The i&ulatLd electrode, Proc. Am Conf. Engineering in M?dicine a?ld Biology, Bomln, MA, U.S.A., 1967. A. J. Lopez and P. C. Rihudson, Capaoitive electrooardiographic and bioelectric electrodes, IEEE Trans. Biomed. Eng., BME-16 (1%9) 99. W. H. Ko and J. Hynwk, Dry electrodes and electrode amplifiers, in H. A. Miller and D. C. Harrison (ads.), Biomedical Electrode Tehcnology, Academic Press, New York, 1974, pp. 169-181. -_ P. Zipp and H. Ahrens, A model of bioelectrode motion artefact and reduction of artefaet by amplifier input stage design, J. Biomed. Eng., 1 (1979) 273-276.
493 TABLE 1. Performance skin electrode
characteristics
17 1 10 d.c. to 75 0.35 2.5 - 15 0.1 500 10 20
Input bias current Input resistance Output resistance Bandwidth Noise voltage Supply voltage Accuracy Max. load resistance Min. load resistance Supply current
-
silver-foil
---
of the microelectronic
___
silver-layer
nA Gohm ohm kHz /W/Hz V % kohm kohm PA
stainlesssteel
100
0.1’ 5
I
“’ 100
10 Frsquency
Fig. 6. Microphotograph
of a chip electrode.
Fig. 8. The noise performance
sponds to the maximum voltage variation of 0.3 mV. The Darlington input transistors, biased at a collector current I, = 0.5 PA, have an input current of about 0.2 nA. The complete circuit of the buffer-amplifier is shown in Fig. 5. The microphotograph of the chip is given in Fig. 6. Table 1 shows a typical performance of the microelectronic skin electrode. The frequency response of the microelectronic skin electrode is shown in Fig. 7. The noise performances of the
60
-
50
-20
(Hz)
of the encapsulated
encapsulation devices are shown in Fig. 8. The noise measurement has been done for three types of substrate cover, i.e. silver foil, stainless steel, and a silver layer of 300 nm. Measurements
The basic structure for the measurements is shown in Fig. 3. To reduce the EMG effects, the two electrodes were placed on the chest of the patient. In this experiment we made ECG measurements using a three-lead system. Different signals between the two microelectronic skin electrodes are detected by an instrument amplifier and are displayed by a digital memory oscilloscope. One metal electrode is applied to the right leg and behaves as common to the two other electrodes. The ECG measurements were made under normal conditions, simultaneously
‘, ,___ ‘..,
-30 -40 1
“““’ 10
-
Fig. 7. The frequency electrode.
100
“_“’ 1000 Frequency
response
“““’ 10000 [Hz1
“““d 100000
“1000000
of the microelectronic
device.
skin Fig. 9. An example
of the ECG results.
494
with the other experiments. A typical result is given in Fig. 9, using stainless steel and silver foil electrodes.
Conclusions
It has been shown that it is possible to make an active dry skin electrode in a standard bipolar process. Motion artifacts are still dominant in the measurement of ECG and can be reduced by higher input impedance and lower input bias current [5]. The noise of the device can be reduced by using a metal layer evaporated on the substrate, as shown by noise performances for the silver layer in Fig. 8. Another version of this new type of active dry skin electrode with P-channel JFETs (junction FETs) is under development. The input impedance of this version will be larger and the input bias current will be smaller, which gives a reduction in the motion artifact effects.
Acknowledgements
The authors wish to acknowledge the process development by the members of DIMES (Dr P. Sarro, Dr L. Nanver, A. Bouwman, R. Maley and J. Groeneweg).
1 G. E. Bergey, R. D. Squires and W. C. Sipple, Electrocardiogram recording with pasteless electrodes, IEEE Trans. Biomed. Eng., EME- 18 ( 197 1) 206. 2 P. C. Richardson, The insulated electrode, Proc. Ann. Conf
Engineering in Medicine and Biology, Boston, MA, U.S.A., 196% 3 A. J. Lopez and P. C. Richardson, graphic
and bioelectric
electrodes,
EME-16 (1969) 99. 4 W. H. Ko and J. Hynecek,
Capacitive
electrocardio-
IEEE Trans. Biomed. Eng.,
Dry electrodes and electrode and D. C. Harrison (eds.), Biomedical Electrode Tehcnology, Academic Press, New York, 1974, pp. 169-181. 5 P. Zipp and H. Ahrens, A model of bioelectrode motion artefact and reduction of artefact by amplifier input stage design, J. Biomed. Eng., I (1979) 273-276. amplifiers,
in H.
A.
Miller