TW444255B - Hydrogen sensor - Google Patents

Abstract

In this invention, we propose a high-sensitivity Pd/InP hydrogen sensor. First, a n-type InP semiconductor membrane is grown on a semi-insulating InP substrate. The concentration and thickness of this membrane are 2x10<SP>17</SP> cm<SP>-3</SP> and 3000 respectively. Then, Pd metal and AuGe alloy are evaporated on the surface of the membrane as the anode and cathode electrodes, respectively. Due to the catalytic performance of Pd metal, the adsorbed hydrogen molecules on the surface of the Pd metal are dissociated into hydrogen atoms. The hydrogen atoms diffuse and pass through the Pd metal and form a dipole layer at the interface between the Pd metal and the n-type InP membrane. This dipole layer will decrease the depletion width of the n-type InP membrane and further lower the metal-semiconductor Schottky barrier height. Therefore, the current-voltage (I-V) characteristics will be modulated after the introduction of hydrogen gas. From the experimental results, the forward and reverse currents in the I-V characteristics of the sensor are both increased with increasing hydrogen concentration in air. The saturation sensitivity can reach to 130 in a 1% hydrogen concentration in air. Furthermore, even a very low hydrogen concentration of 200 ppm in air is introduced, a saturation sensitivity of 2 is obtained. This reveals that the invention is a high sensitivity hydrogen sensor.

Description

'4442 5 5 5. Description of the invention (1) Field of the invention The present invention relates to a high-sensitivity hydrogen sensor, and in particular to a target / indium phosphide (Pd / ΙηΡ) chlorine gas sensor, which has a small volume The advantages of simple process. BACKGROUND OF THE INVENTION In the emphasis on leaking hydrogen as a raw material, there is an explosion of concern. In addition to the need for the detector to reach the risk of intelligent motion components in technology or other gas and air explosions, hydrogen accurately measures the volume of the hydrogen. , The current use, and the concentration of hydrogen is dangerous. Therefore, the sensor has been widely known for leaking hydrogen, high cost equipment or conversion requirements. Therefore, the sensor is a contemporary industrial gas. It is once based on the content of industrial and industrial use, the large circuit and medical species are flammable to reach 4. Occupational safety is used for work, but some of it can be carried out. The development of a new type of today's important task and an explosion of 65 5 vo 1 are considered in the factory. It is currently in a passive analysis or a valid question. When the gas is more than%, the traditional hydrogen sensing element of environmental protection laboratory and hospital still enlarges the 'impossible smart master in recent years'. The research of MOS (metal-oxide-semiconductor) structure as a semiconductor hydrogen sensor has attracted many people's interest. The reason why the metal is used in its structure is that palladium has good catalytic activity. In the environment containing hydrogen, it can dissociate hydrogen molecules adsorbed on the surface into hydrogen atoms, and some of the hydrogen atoms will diffuse through the palladium metal and adsorb. After polarization of these milk atoms at the boundary between the metal and the oxide layer, the Schottky barrier height at the interface between the oxide layer and the Shi Xi semiconductor will be changed, and the electrical properties of the device will be changed accordingly. in

Page 7 4442 5 5 5. Description of the invention (2) Early I. Lundstrom proposed palladium gate palladium / silicon dioxide / J5 field effect transistor ^^ Pd / Si02 / S i MOS field effect transistor) [Lundstrom, MS Shi varaman, and C. Sven sson, J. Appl. Phys., 46, 3876 (1975)] 'The change in threshold voltage and capacitance value at both ends after using the gate to absorb hydrogen' is used as a test The two basis of hydrogen "But the use of three-terminal elements to realize the functions of two-terminal elements is not only cost-effective, but also increases the difficulty of the process. In addition, the quality of the oxide layer is also related to the quality of the hydrogen sensing ability, in addition to reliability issues In addition, when the growth of the oxide layer is contaminated by ionic contamination or increased defects, the Fermi level of silicon semiconductors will have a surface state pinning of Fermi-level. At this time, Schottky The barrier height is less affected by polarized hydrogen atoms, so the sensitivity to hydrogen is also poor. Many studies have improved this problem, for example, A. Dutta et al. Used zinc oxide (Zη〇) and others [A. Dutta, T . Κ.

Chaudh ur i, and S. Basu, Materials Science Engineering, B14, 31 (1992)] and L. Yadava et al. [L. Yadava, R. Dwivedi, and S. K. Srivastava,

Solid-St. Electron., 33, 1229 (19 9 0)] replaces the silicon dioxide oxide layer with titanium dioxide (Ti02). On the other hand, if it is implemented with a Schottky barrier diode at both ends, it seems to be a more intuitive approach. The instability of the oxide layer is reduced, and the sensitivity to hydrogen is significantly improved. In the early days, such as MC Steele and others proposed the structure of palladium / diffusion (Pd / CdS) [MC Steeie and BA Maciver, Appl. Phys. Lett., 28, 687 (1 976)] and K. Ito and others

444255 V. Description of the invention (3) Palladium / zinc oxide (Pd / ZnO) structure [K_It〇, SurfaceSci., 86, 345 (1 982)], why use ii-VI grouping, house semiconductors as materials, The main reason is that the surface state of the ι-νι compound semiconductors is not as significant as that of polarized hydrogen atoms. SUMMARY OF THE INVENTION The main object of the present invention is to provide a high-sensitivity hydrogen sensor including: a semiconductor substrate; an n-type or mouth-type semiconductor thin film formed on a rhenium semiconductor substrate; and a On the same surface but spaced apart from each other = an anode and a cathode, wherein a first metal as an anode makes a Schottky contact with the semiconductor rhenium film, and a second metal as a cathode makes ohmic contact with the semiconductor film Wherein, the material and thickness of the first metal can reduce the height of the Schottky barrier of the Schottky contact when the hydrogen contacts an exposed surface of the first metal. ^ In the hydrogen sensor of the present invention, the first metal material and thickness are such that when hydrogen contacts the exposed surface of the first metal, the hydrogen is dissociated into ^ atoms' and the hydrogen atoms diffuse through the first A metal, thus reducing the Schottky barrier height. Preferably, the first metal is a handle or a palladium alloy, and more preferably palladium. The 1 bar, preferably &apos; has a thickness of 2000 angstroms to 5 microns. In the hydrogen sensor of the present invention, it is preferable that the semiconductor substrate is formed of a semi-insulating indium phosphide (I np) material.

444 2 b V. Description of the invention (4) ---- In the hydrogen sensor of the present invention, preferably, the semiconductor thin η-type IH-V group compound is more preferably indium dished (η_ίηρ). ^ 'Is a suitable doping degree for η InP ranging from ΐχΐ〇] 6 to 5χΐ〇ρ cnr3, and a suitable thickness ranging from 1000 Angstroms to 5Gangstroms. In the hydrogen sensor of the present invention, the second metal is preferably gold germanium sigma gold (AuGe). The gold-germanium alloy preferably has a thickness between 5 microns. In the hydrogen sensor of the present invention, preferably, the anode has a C-shape or a C-like shape, and the cathode has a shape corresponding to the anode so that the cathode is surrounded by the anode. Alternatively, the cathode has a c-shape or a C-like shape, and the anode has a shape corresponding to the cathode such that the anode is surrounded by the cathode. Development ^-A palladium / indium phosphide gas sensor completed in accordance with a preferred embodiment of the present invention: the use of palladium as a catalyst metal to dissociate hydrogen molecules into hydrogen = The force of the interface between the indium thin film and the palladium metal that can adsorb a large number of hydrogen atoms results in a significant linear change in the electrical properties of the diode, and thus can detect low-concentration hydrogen content. In order to make it clearer, the purpose, features, and advantages of the invention are more obvious and easy to understand, a preferred embodiment will be given below, and it will be described in detail with the accompanying drawings of the present invention. Detailed description of a preferred embodiment A highly sensitive palladium / indium phosphide hydrogen sensor completed in accordance with a preferred embodiment of the present invention includes:-a semi-insulating indium phosphide-based

Page 10 4442 5 5

Plate; a Π-type indium phosphide film located on the semi-insulating indium phosphide substrate; an ohmic contact metal layer of a gold-germanium alloy and a Schottky contact metal layer of a palladium metal 'are adjacent to each other but isolated, and are located in the phosphorus On indium thin film. ^ In the high-sensitivity palladium / indium phosphide hydrogen sensor, the n-type indium phosphide thin gadolinium system is grown on the semi-insulating scaled indium substrate by using organometallic vapor deposition (MOCVD). The n-type scaled indium thin film, so it has a reduced surface state potential density. The Schottky Moon b barrier between metal and semiconductor has a close relationship with the number of polarized hydrogen atoms, that is, the surface state potential density. In addition, the hydrogen coverage of the indium phosphide material is 1¾, and the relatively low gas content in the air can also significantly change the Schottky energy IV dimension. This characteristic is suitable as a low degree of less than one percent. Detection. In terms of temperature characteristics, the bandgap of the indium phosphide material is about 1.35, which is larger than that of silicon, and also has good temperature resistance performance. In addition, most importantly, the indium phosphide material growth and process technology has matured. Helmets are photovoltaic or microwave integrated circuits that have been used in the industry. The hydrogen sensor of the present invention can be integrated and integrated with photovoltaic elements. It will become a multi-functional intelligent sensor that detects both photoelectricity and hydrogen at the same time. It is believed that future applications in various aspects will have great potential. EXAMPLES A high-sensitivity handle / indium phosphide hydrogen sensor i 0 completed according to a preferred embodiment of the present invention is shown in the first figure. The preparation method includes three pieces, and half of the insulating indium phosphide is prepared. Board 丨 2. Secondly, the technique of organic metal chemical vapor deposition was used to form the semi-insulating indium phosphide substrate 2

Page 114442 55 V. Description of the invention (6) A long-quality η-type indium phosphide film 丨 4, the concentration and thickness of which are 2xlOncnr3 and 3000 禳 C, respectively. Then, the traditional photolithography and vacuum evaporation are used. In the technology, the ohmic contact metal layer 16 of gold-germanium alloy and the Schottky contact metal layer 18 of palladium metal are vapor-deposited on the surface of the n-type indium phosphide film μ, respectively, as the cathode and anode of the sensor, respectively. The charge density distribution and cross-sectional energy band diagram of the sensor of the present invention in the first figure when (a) no hydrogen is sensed and (b) when hydrogen is sensed are shown in the second figure. Before the introduction of hydrogen, the charge distribution at the interface of the sensor's palladium metal 8 and n-type indium phosphide film 1 4 is in equilibrium, and a metal-semiconductor Schottky barrier is formed, as shown in the second figure ( a) shown. After the introduction of argon, because palladium metal 18 has a catalytic effect on hydrogen, when hydrogen molecules are adsorbed on the surface of palladium metal, they will be dissociated into hydrogen atoms, and most of the hydrogen atoms will diffuse through palladium. A dipole moment layer is formed between the interface of the metal 18 and the n-type indium phosphide film 14 'This moment of a dipole moment will change the equilibrium state of the original charge distribution and reach a new equilibrium state' This new equilibrium The state reduces the width of the empty region of the n-type phosphide semiconductor, thereby reducing the Schottky barrier height, as shown in the second figure (b). The third figure is a current-voltage characteristic curve diagram of the sensor of the present invention in air and air containing different hydrogen contents (200ppm, 500ppm, 100ppm, 5000ppm, 1000ppm) in environmental measurement. The forward bias in this figure is interpreted as the positive voltage applied to the Schottky contact relative to the ohmic contact, and the negative voltage applied to the reverse ground 'reverse bias. The larger the hydrogen content is, the smaller the Schottky barrier height is, the larger the current is. It can be seen from the figure that both the forward biased current and the reverse biased current follow the hydrogen in the air.

Page 12 4442 5 5 V. Description of the invention (7) Increasing with increasing gas content 'Among them, it is more obvious that the increasing trend of reverse current is a linear increase in proportion to the hydrogen content. The fourth graph shows the relationship between the Schottky barrier height of the sensor of the present invention and the hydrogen content in the air in the first graph. The energy barrier height in the air is about 50 meV. The barrier height gradually decreases. When the hydrogen content is greater than 0.5%, the barrier height reaches almost the lowest value. At this time, the forward current conduction is very close to the ohmic characteristic. The fifth graph is the transient response graph of the sensor of the present invention measured at the temperature of 125 ° C in the first graph. When hydrogen is introduced, air representing 200 ppm of hydrogen content flows into the test chamber at a rate of 500 ml / min. The test conditions are maintained between the Schottky contact metal layer 18 and the ohmic contact metal layer η of the palladium metal. A fixed reverse current of 8πA, because the dissociated hydrogen atoms form a dipole moment layer, the reverse current through the Schottky contact increases, thus causing the voltage between the two electrodes to decrease relatively! 2V 'On the other hand, when the hydrogen is turned off, the sensor is directly exposed to the air, and the hydrogen atoms are combined into hydrogen molecules or the water molecules are combined into water molecules to desorb the surface of the palladium metal, thus causing a voltage recovery between the two electrodes. . If the reaction time and the recovery time are defined as the time required to reach individual stability = 0%, it can be seen from the figure that the response time of the sensor is about the same amount: the return and return interval is about 12 seconds. In addition, repeating the measurement of the first-period, it was found that it showed a fairly high reproducibility in both the second and the sixth periods. The sixth graph is a graph of the hydrogen content relationship in the first graph. Under voltage, the saturation sensitivity of the sensor of the present invention flowing through the two electrodes versus air immunity and sensitivity S are defined as the ratio of the current change to the reference current (1 ^

Page 13 4442 5 5 V. Description of the invention (8) _1 $ gas) / 1 air 'It is obvious from the figure that the sensitivity increases with the increase of hydrogen content. Under 0.5V reverse bias, the saturation sensitivity measured in the air with 1% hydrogen content can reach 130, and the saturation sensitivity measured in the air with a relatively low 20001 ~ 111 hydrogen content can also reach 2. From the above, it can be known that, in addition to the advantages of small volume, simple process, and integration, the hydrogen sensor of the present invention shows that its high linearity, high response speed, high reproducibility, and high sensitivity. This feature is also far superior to the traditional hydrogen sensor in general. If it can be mass-produced and reduce costs, the hydrogen sensor of the present invention will be extremely useful in industrial safety. Although the present invention has been limited to the following: Anyone who is familiar with this skill can use various changes and modifications within the scope of :::, so this issue: &quot; Only the scope shall be determined by the scope of the attached patent application.

Brief description of the drawings Brief description of the circles: The first diagram is a schematic diagram of a palladium / disdium indium hydrogen sensor completed according to a preferred embodiment of the present invention. The second diagram is the charge density distribution and cross-section energy band diagram of the palladium / indium phosphide hydrogen sensor in the first diagram when (a) no hydrogen is sensed and (b) hydrogen is sensed. The third picture is measured in the first picture of the palladium / indium phosphide hydrogen sensor in air and air containing different argon content (200ppm, 500ppm, 1000ppm, 50,000 ppm, 100 ppm) Current-voltage characteristic curve. The fourth picture is the relationship between the Schottky barrier height and the hydrogen concentration of the palladium / indium phosphide hydrogen sensor in the first picture. Transient response diagram measured at a temperature of 1 2 5 ° c. The sixth diagram is the relationship between saturation sensitivity and hydrogen content of the palladium / indium phosphide gas sensor in the first diagram. The symbols in the diagram indicate: 10 Hydrogen sensor 12 Semi-insulating indium phosphide substrate 14 η Type indium phosphide film 16 Ohmic contact metal layer of gold alloy 18 Schottky contact metal layer of palladium metal

Claims (1)

4442 55 6. Scope of patent application I. A hydrogen sensor including a semiconductor substrate; n-type or? Formed on the semiconductor substrate? Type semiconductor thin film; and an anode and a cathode formed on the same surface of the semiconductor semiconductor film but spaced from each other, wherein a first metal serving as an anode forms a Schottky contact with the semiconductor film, and a cathode serving as a cathode A second metal makes ohmic contact with the semiconductor thin film, wherein the material and thickness of the first metal can make the Schottky barrier height of the Schottky contact decrease when hydrogen contacts an exposed surface of the first metal. 2. The argon gas sensor according to item 1 of the patent application scope, wherein the material and thickness of the first metal are such that when hydrogen contacts the exposed surface of the first metal, the 'argon gas is dissociated into hydrogen atoms, and the hydrogen Atomic diffusion penetrates the first metal, thereby reducing the Schottky barrier height. 3 _ The argon gas sensor according to item 1 of the patent application, wherein the semiconductor substrate is formed of a semi-insulating indium phosphide (nP) material. 4. The hydrogen sensor according to item 1 of the patent application, wherein the semiconductor thin film is a η-type I 11 -V group compound. 5. The hydrogen sensor 'according to item 4 of the patent application, wherein the n-type III-V group compound is 11-type 111 卩. — — Page 16 4442 55 6. Scope of patent application 6. For example, the hydrogen sensor of item 5 of the scope of patent application, wherein the 11-type InP has a doping concentration between lx1016 and cm-3. 7. The hydrogen sensor according to item 5 of the patent application, wherein the n-type InP has a thickness between 1000 angstroms and 5000 angstroms. 8. The hydrogen sensor according to item 1 of the patent application scope, wherein the first metal is a Syrian or Ki alloy. 9. The hydrogen sensor according to item 8 of the patent application, and the first hydrogen sensor in the first application, wherein the thickness of the period 10 to 10 is from 2000 angstroms to 5 microns. Belongs to 11 _ If the scope of patent application for the i series is AuGe. The hydrogen sensor of item 2, the second gold 1 2 _ As in item 11 of the scope of patent application, the germanium alloy has a hydrogen sensor with a thickness of 3,000 angstroms, wherein the thickness is 5 micrometers. Gold 13. If the scope of patent application is the first! The hydrogen sensor of the item has a -C shape or a shape similar to the C shape, and the shape of the cathode makes the cathode an anode. $ T 应 于 心 Page 17 4442 55 VI. Patent application scope 14. The hydrogen sensor of item 1 of the patent application scope, wherein the cathode has a C-shape or similar C-shape, and the anode has a shape corresponding to the shape of the cathode. The anode is surrounded by the cathode. Page 18