CN110459471B - Preparation method of GaN-based pH sensor with double-gate structure - Google Patents
Preparation method of GaN-based pH sensor with double-gate structure Download PDFInfo
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Abstract
The invention relates to the technical field of semiconductor sensors, in particular to a preparation method of a GaN-based pH sensor with a double-gate structure. The method comprises the following steps: s1, growing a high-resistance insulated GaN transition layer on an n-type GaN substrate to serve as a medium layer of a back gate; s2, growing a GaN channel layer on the high-resistance insulated GaN transition layer; s3, growing an AlGaN thin barrier layer on the surface of the channel layer; s4, depositing an ohmic contact electrode; s5, growing a medium layer to cover the electrode and exposing the access area to the top gate detection area. The invention provides a preparation method of a double-grid structure GaN-based pH sensor, which comprises the steps of growing a thin potential barrier AlGaN layer, and utilizing a silicon nitride passivation layer to cover the part outside a sensing area to improve the two-dimensional electron gas concentration and the mobility of an access area; by utilizing the thin barrier layer structure, high transconductance can be realized, and the detection sensitivity breaking through the Nernst limit is obtained by combining the capacitive coupling effect of the back gate electrode and the channel.
Description
Technical Field
The invention relates to the technical field of semiconductor sensors, in particular to a preparation method of a GaN-based pH sensor with a double-gate structure.
Background
The pH sensor is a necessary inspection device for measuring the pH value of a liquid medium, performing precise monitoring and scientific certification, and has important application in the field of using solutions in environment, medical treatment, industry, agriculture, biology and the like. With the continuous development of science and technology, all-solid-state pH sensors based on Ion Sensitive Field Effect Transistors (ISFETs) are favored because of their small size, non-fragility, high sensitivity, stable performance, portability, and the like. At present, Si-based MOSFET is the main material for preparing ISFET pH sensor due to its characteristics of low price, compatibility with traditional CMOS process, mass production, good reliability, etc. However, the development of Si-based pH sensors gradually approaches to the theoretical limit, and because the performance defects of the materials themselves cannot work in high temperature (lower than 150 ℃) and some specific solution (hydrofluoric acid and the like) environments, the stability and reliability of the pH sensors cannot be guaranteed, and the practicability of the pH sensors is greatly limited.
Recently, common ISFETs are gradually expanding from typical Si-based ISFETs to III-nitride-based ISFETs and oxide semiconductor TFT-based ISFETs. Compared with a glass electrode, the ISFET does not need a built-in reference electrode, the structure of the device is simplified, a miniaturized detector is facilitated to be realized, the test convenience is improved, and the silicon-based mature semiconductor processing technology is utilized to facilitate large-scale production. Group III nitride materials have a wider band gap and greater chemical stability, which makes them more resistant to extreme conditions (e.g., high temperature), and group III nitride materials are more biocompatible than silicon-based materials, which makes group III nitride ISFETs of great interest.
Although GaN-based ISFET pH sensors have a wide application prospect, their sensitivity is still limited. To improve the sensitivity of pH sensors, different high-k oxide materials have been investigated as the sensitive layer of ISFETs (e.g., Al)2O3、Er2O3、HfO2、Ta2O5、HoTiO3、Pr2O3Etc.) so that the sensitivity of the ISFET-pH probe approaches 59 mV/pH. However, its sensitivity is still limited by the Nernst limit, so that it can only be achieved at 298K with a maximum sensitivity of 59 mV/pH. In order to break through the sensitivity limit, a plurality of domestic and foreign research teams provide a high-sensitivity double-gate transistor sensor structure aiming at the silicon and oxide sensor, and the high-sensitivity double-gate pH detector can be realized through the capacitive coupling amplification effect between the top gate and the bottom gate of the transistor. This is because oxide can be deposited on a silicon oxide/conductive silicon substrate and a material with excellent crystalline quality is obtained. However, GaN cannot realize heteroepitaxy on a silicon oxide/conductive silicon substrate at present, and dislocation defects with high density exist in the material, which hinders the realization of the dual-gate type sensor.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides a preparation method of a GaN-based pH sensor with a double-gate structure, which can realize high transconductance.
In order to solve the technical problems, the invention adopts the technical scheme that: a double-gate structure GaN-based pH sensor preparation method combines the capacitive coupling effect of a back gate electrode and a two-dimensional electronic gas channel to obtain detection sensitivity breaking through the Nernst limit; the method specifically comprises the following steps:
s1, growing a high-resistance insulated GaN transition layer on an n-type GaN substrate to serve as a medium layer of a back gate;
s2, growing a GaN channel layer on the high-resistance insulated GaN transition layer;
s3, growing an AlGaN thin barrier layer on the surface of the channel layer; the thickness of the AlGaN thin barrier layer is 0-20 nm;
s4, depositing an ohmic contact electrode;
s5, the ohmic contact electrode and the access area on the thin barrier layer are covered by the growth medium layer, and the top gate detection area is exposed on the thin barrier layer.
According to the invention, an intrinsic GaN epitaxial layer is formed on a highly doped GaN single crystal substrate by controlling growth parameters to replace a dielectric layer, so that a thin barrier layer AlGaN/GaN structure is grown to improve the transconductance of the device, and the barrier layer and the ohmic contact electrode outside a detection region are covered by SiN to recover an access region to improve the electron concentration and the mobility of a device channel.
Further, the high-resistance insulating GaN transition layer and the AlGaN/GaN heterojunction material with smaller thickness of the thin barrier grown in the steps S1 to S3 are provided.
Further, by depositing silicon nitride in the step of S5, the ohmic contact electrode (5) is simultaneously protected and the part outside the detection region is covered.
Further, the substrate is any one of GaN self-supporting substrates grown by an ammonothermal method, HVPE or MOCVD; the high-resistance insulating GaN transition layer is any one or combination of AlN, AlGaN and GaN; the thickness is 10 nm-10 mu m; the dielectric layer is silicon nitride and has a thickness of 0-500 nm.
Furthermore, the GaN channel layer is an unintentionally doped GaN epitaxial layer or a doped high-resistance GaN epitaxial layer, and the doped element of the GaN channel layer is carbon or iron; the thickness of the GaN channel layer is 100 nm-20 μm.
Furthermore, the AlGaN thin barrier layer is low-aluminum-component AlGaN, and the concentration of the aluminum component is between 0 and 15 percent.
Furthermore, the AlGaN thin barrier layer can also be made of one or a combination of any of AlInN, InGaN, AlInGaN and AlN.
Furthermore, the ohmic contact electrode material is Ti/Al/Ni/Au alloy, Ti/Al/Ti/Au alloy, Ti/Al/Mo/Au alloy or Ti/Al/Ti/TiN alloy, and the electrode thickening metal material is Ni/Au alloy, In/Au alloy or Pd/Au alloy.
Furthermore, an AlN thin layer with the thickness of 1-10nm can be inserted between the AlGaN thin barrier layer and the GaN layer.
Further, the growth methods of the high-resistance insulating GaN transition layer in the step S1, the GaN channel layer in the step S2, and the AlGaN thin barrier layer in the step S3 are metal organic chemical vapor deposition, molecular beam epitaxy; the method for growing the dielectric layer in step S5 is a plasma enhanced chemical vapor deposition method, an atomic layer deposition method, a physical vapor deposition method, or a magnetron sputtering method.
Compared with the prior art, the beneficial effects are: the invention provides a preparation method of a double-grid structure GaN-based pH sensor, which comprises the steps of growing a thin barrier AlGaN layer, covering the part outside a detection region by a silicon nitride passivation layer, and improving the concentration and the mobility of two-dimensional electron gas below the AlGaN contact region; by utilizing the thin barrier layer structure, high transconductance can be realized, and the detection sensitivity breaking through the Nernst limit is obtained by combining the capacitive coupling effect of the back gate electrode and the channel.
Drawings
Fig. 1 to fig. 5 are process schematic diagrams of a device manufacturing method according to embodiment 1 of the present invention.
Fig. 6 is a schematic structural diagram of a device provided in embodiment 2 of the present invention.
Detailed Description
The drawings are for illustration purposes only and are not to be construed as limiting the invention; for the purpose of better illustrating the embodiments, certain features of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted. The positional relationships depicted in the drawings are for illustrative purposes only and are not to be construed as limiting the invention.
Example 1:
as shown in fig. 1 to 5, a dual-gate structure GaN-based pH sensor comprises a substrate 1, a transition layer 2, a channel layer 3, a barrier layer 4, an ohmic contact electrode 5, and a dielectric layer 6 in sequence from bottom to top; the preparation method specifically comprises the following steps:
s1, growing a high-resistance insulating GaN transition layer 2 on an n-type GaN substrate 1 as a dielectric layer of a back gate;
s2, growing a GaN channel layer 3 on the high-resistance insulated GaN transition layer 2;
s3, growing an AlGaN thin barrier layer 4 on the surface of the channel layer 3; the AlGaN thin barrier layer 4 is 0-20 nm thick;
s4, depositing an ohmic contact electrode 5;
s5, a growth medium layer 6 covers the ohmic contact electrode 5 and the access area on the thin barrier layer 4, and the top gate detection area is exposed on the thin barrier layer 4.
According to the invention, an intrinsic GaN epitaxial layer is formed on a highly doped GaN single crystal substrate by controlling growth parameters to replace a dielectric layer, so that a thin barrier layer AlGaN/GaN structure is grown to improve the transconductance of the device, and the barrier layer and the ohmic contact electrode outside a detection region are covered by SiN to recover an access region to improve the electron concentration and the mobility of a device channel.
Specifically, the GaN intermediate layer 2 with high resistance and insulation and the AlGaN/GaN heterojunction material with smaller thickness are grown in the steps S1 to S3.
Wherein the ohmic contact electrode 5 is simultaneously protected and covered at the outside of the detection region by depositing silicon nitride in said step S5.
In addition, the substrate is any one of GaN self-supporting substrates grown by an ammonothermal method, HVPE or MOCVD; the high-resistance insulating GaN transition layer is any one or combination of AlN, AlGaN and GaN; the thickness is 10 nm-10 mu m; the dielectric layer is silicon nitride and has a thickness of 0-500 nm. The GaN channel layer is an unintentionally doped GaN epitaxial layer or a doped high-resistance GaN epitaxial layer, and the doping element of the GaN channel layer is carbon or iron; the thickness of the GaN channel layer is 100 nm-20 μm. The AlGaN thin barrier layer is low-aluminum-component AlGaN, and the concentration of the aluminum component is between 0 and 15 percent. The AlGaN thin barrier layer material can also be one or the combination of any of AlInN, InGaN, AlInGaN and AlN. The ohmic contact electrode material is Ti/Al/Ni/Au alloy, Ti/Al/Ti/Au alloy, Ti/Al/Mo/Au alloy or Ti/Al/Ti/TiN alloy, and the electrode thickening metal material is Ni/Au alloy, In/Au alloy or Pd/Au alloy.
Wherein, an AlN thin layer with the thickness of 1-10nm can be inserted between the AlGaN thin barrier layer and the GaN layer.
In addition, the growth methods of the high-resistance insulating GaN transition layer in the step S1, the GaN channel layer in the step S2, and the AlGaN thin barrier layer in the step S3 are a metal organic chemical vapor deposition method and a molecular beam epitaxy method; the method for growing the dielectric layer in step S5 is a plasma enhanced chemical vapor deposition method, an atomic layer deposition method, a physical vapor deposition method, or a magnetron sputtering method.
Example 2
As shown in fig. 6, is a schematic view of the device structure of this embodiment, which is different from the structure of embodiment 1 only in that: in the embodiment 1, an induction enhancement film 7 is added on the grid region, so that the detection sensitivity of the device is further improved.
It should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.
Claims (9)
1. A method for preparing a GaN-based pH sensor with a double-gate structure is characterized in that a thin barrier layer (4) structure is utilized to realize high transconductance; by combining the capacitive coupling effect of the back gate electrode and the channel, the detection sensitivity breaking through the Nernst limit is obtained; the method specifically comprises the following steps:
s1, growing a high-resistance insulated GaN transition layer (2) on an n-type GaN substrate (1) to serve as a dielectric layer of a back gate;
s2, growing a GaN channel layer (3) on the high-resistance insulated GaN transition layer (2);
s3, growing an AlGaN thin barrier layer (4) on the surface of the channel layer (3); the thickness of the AlGaN thin barrier layer (4) is 0-20 nm;
s4, depositing an ohmic contact electrode (5);
s5, a growth medium layer (6) covers the ohmic contact electrode (5) and the access area on the thin barrier layer (4), and only the top gate detection area is exposed on the thin barrier layer (4).
2. The method of claim 1, wherein the ohmic contact electrode (5) is protected and covers the part outside the sensing region by depositing silicon nitride in step S5.
3. The method for manufacturing the double-gate structure GaN-based pH sensor according to claim 1, characterized in that the substrate (1) is any one of a GaN free-standing substrate (1) grown by ammonothermal method, HVPE or MOCVD; the high-resistance insulating GaN transition layer (2) is any one or combination of AlN, AlGaN and GaN; the thickness is 10 nm-10 mu m; the dielectric layer (6) is made of silicon nitride and has the thickness of 0-500 nm.
4. The method for manufacturing the double-gate structure GaN-based pH sensor according to claim 1, wherein the GaN channel layer (3) is an unintentionally doped GaN epitaxial layer or a doped high-resistance GaN epitaxial layer, and the doping element of the GaN channel layer (3) is carbon or iron; the thickness of the GaN channel layer (3) is 100 nm-20 μm.
5. The method of claim 1, wherein the AlGaN thin barrier layer (4) is AlGaN with a low Al content and the Al content is between 0-15%.
6. The method for manufacturing the double-gate GaN-based pH sensor according to claim 5, wherein the AlGaN thin barrier layer (4) is made of one or a combination of AlInN, InGaN, AlInGaN, and AlN.
7. The method for manufacturing the GaN-based pH sensor with the double gate structure according to any of claims 1-6, wherein the ohmic contact electrode (5) is made of Ti/Al/Ni/Au alloy, Ti/Al/Ti/Au alloy, Ti/Al/Mo/Au alloy or Ti/Al/Ti/TiN alloy, and the electrode thickening metal material is Ni/Au alloy, In/Au alloy or Pd/Au alloy.
8. The method of claim 7, wherein an AlN thin layer is inserted between the AlGaN thin barrier layer (4) and the GaN layer, and the thickness of the AlN thin barrier layer is 1-10 nm.
9. The method of claim 7, wherein the growth methods of the high-resistance insulating GaN transition layer (2) in step S1, the GaN channel layer (3) in step S2, and the AlGaN thin barrier layer (4) in step S3 are MOCVD or MOE; the method for growing the dielectric layer (6) in the step S5 is a plasma enhanced chemical vapor deposition method, an atomic layer deposition method, a physical vapor deposition method or a magnetron sputtering method.
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