JP4461643B2 - Charged particle detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a charged particle detection apparatus that obtains the concentration of charged particles (for example, negative ions, positive ions, viruses, bacteria, etc. in a liquid) using an electric field effect.
[0002]
[Prior art]
A conventional charged particle detector is shown in FIG. As shown in this figure, the charged particle detection device includes a cylindrical rod-shaped electrode J1, and a cylindrical electrode J2 that is insulated from the rod-shaped electrode J1 so as to be concentric with the rod-shaped electrode J1. The
[0003]
In such an apparatus, the concentration of charged particles and the like are determined based on voltage and current. For example, when calculating | requiring based on a voltage, an electric charge is beforehand stored between both electrodes by grounding one electrode and turning ON switch J3 first. Then, the charged particles are circulated in the cylinder for a certain period of time after the switch J3 is turned off, thereby measuring the change in voltage with respect to time, that is, the potential drop corresponding to the neutralization amount of the charge by the charged particles, and obtaining the concentration of the charged particles. It has become. On the other hand, in the case of obtaining based on the current, if the replenishment current is applied so that the voltage is constant, the replenishment current and the charged particles have a 1: 1 relationship. The concentration of particles is calculated.
[0004]
[Problems to be solved by the invention]
However, the conventional charged particle detection device has a problem that it is large in size and heavy, so that it is not easy to incorporate into various devices and the cost is high.
[0005]
The present invention has been made in view of the above points, and an object of the present invention is to provide a charged particle detection device that is small and lightweight and can be easily incorporated into various devices.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, according to the first to third aspects of the present invention, the semiconductor substrate (2) and the source region (3) and the drain region (4) formed so as to be separated from each other in the surface layer portion of the semiconductor substrate. When a channel is formed between the source region and the drain region, a floating gate (6) formed with an exposed portion that comes into contact with the outside air on the channel, and a control gate (8) for controlling the potential of the floating gate And a tunnel film (7) disposed between the floating gate and the control gate.
[0007]
According to such a configuration, the charged particle detection device can be realized with a structure that is small and lightweight and can be easily incorporated into various devices. For example, as shown in claim 3, by adjusting the potential of the control gate so that the current (I _DS ) between the source region and the drain region is constant, the charged particles are controlled based on the potential of the control gate. It is possible to determine the concentration.
[0008]
In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 1 shows a cross-sectional structure of a field effect transistor type charged particle detector 1 to which an embodiment of the present invention is applied. Hereinafter, the configuration of the charged particle detector 1 will be described with reference to FIG.
[0010]
As shown in FIG. 1, the charged particle detector 1 is formed using a silicon substrate 2. A source region 3 and a drain region 4 are formed on the surface layer portion of the silicon substrate 2 so as to be separated from each other. A source electrode 3a and a drain electrode 4a are formed on the surfaces of the source region 3 and the drain region 4, respectively. Has been.
[0011]
When the channel region is defined between the source region 3 and the drain region 4, an insulating film 5 is patterned on the channel region. On the surface of the insulating film 5, there are provided a floating gate 6 made of gold or the like, a tunnel film 7, a control gate 8 made of gold or aluminum or the like, and a sidewall oxide film 9. The floating gate 6 is disposed so as to be exposed to the outside, and the tunnel film 7, the control gate 8, and the sidewall oxide film 9 are sequentially disposed on both side walls of the floating gate 6.
[0012]
The charged particle detection apparatus 1 configured as described above can detect the concentration of charged particles and the like as follows.
[0013]
First, when a voltage is applied so that the control gate-source voltage V _CGS becomes positive, the electrons of the floating gate 6 are extracted and the floating gate 6 is positively charged. _Assuming that the voltage between the floating gate and the source at this time is V _FGS , the charge amount of the floating gate 6 is q, and the electric capacity between the control gate and the source is c, the relationship shown in Equation 1 is established.
[0014]
[Expression 1]
V _FGS = q / c
In this state, a channel is formed between the drain and the source, and a constant current I _DS flows. Even if the potential V _CGS between the control gate and the source is set to 0, charges are stored in the floating gate 6, and the floating gate 6 continues to be positively charged.
[0015]
In such a state, when particles having a negative charge are present in the outside air, the particles are adsorbed to the floating gate 6 and the charge in the floating gate 6 is neutralized. As a result, the floating gate-source voltage V _FGS decreases. The amount of decrease δV _FGS of the voltage V _{GS at} this time is expressed as shown in Equation 2, where q ′ is the amount of absorbed charge.
[0016]
[Expression 2]
δV _FGS = (q−q ′) / c
Then, the charged amount of particles is attracted to the floating gate 6, as it relates to the amount of charged particles present in the atmosphere, the floating gate - decrease in current I _DS caused thereby and decrease in the source voltage V _FGS charged particle Will show the amount.
[0017]
On the other hand, if the voltage is continuously applied to the control gate 8 so that the decrease amount δV _FGS of the voltage V _GS becomes zero, the control gate-source voltage V _{CGS at} this time is the charged particles adsorbed per unit time. Therefore, the charge amount of the charged particles can be obtained based on the voltage V _CGS .
[0018]
In such a case, the control gate 8 itself can be used as the adsorption electrode instead of the floating gate 6. However, if the floating gate 6 is used as the adsorption electrode as described above, the floating gate 6 to the control gate 8 due to the tunnel phenomenon. Since the movement of the charge to the surface occurs and the amount of the movement charge changes exponentially, the effect of increasing the sensitivity to the low concentration of the adsorbed charged particles can be obtained.
[0019]
In other words, the tunnel current has a characteristic that it does not flow unless a large voltage is applied, but it flows in a magnitude according to the voltage, and increases exponentially when the applied voltage is increased. The tunnel current can be controlled, and the sensitivity is increased as described above.
[0020]
Next, FIG. 2 shows an example of a charged particle detection circuit using the charged particle detection device 1 shown in FIG. This detection circuit detects the charge amount of the charged particles based on the control gate-source voltage V _CGS of the charged particle detector 1, and outputs the voltage V _CGS while keeping the source-drain current _IDS constant. A low-pass filter 12 is connected to the low current circuit 10 via a resistor 11 to take measures against noise.
[0021]
The low current circuit 10 includes a constant voltage source 13 so that a desired voltage is applied to the control gate 8 and the drain electrode 4a. The transistor 14 of the switch for controlling the voltage applied to the control gate 8, a source of a charged particle detector 1 - and resistor 15 for controlling the ON / OFF of the transistor 14 is provided on the basis of the drain current I _DS The transistor 14 is controlled based on the voltage drop across the resistor 15.
[0022]
The low pass filter 12 includes an operational amplifier 16, a capacitor 17, and resistors 18 and 19. The non-inverting input terminal of the operational amplifier 16 is connected to the virtual GND through the resistor 19 so that 0 V or less can be output even if the operational amplifier 16 is a single power supply.
[0023]
The charged particle detection circuit having such a configuration operates as follows. First, when the current I _DS increases and the voltage drop at the resistor 15 connected to the source electrode 3a becomes approximately 0.7 V, the transistor 14 is turned on, the voltage V _CGS decreases, and the current I _DS also decreases. When the current I _DS decreases and the voltage drop across the resistor 15 falls below 0.7V, the transistor 14 is turned off, the voltage V _CGS increases, and the current I _DS also increases. Thus the current I _DS is kept constant, because it is controlled so that the decrease amount .DELTA.V _GS of the voltage V _GS becomes 0, the adsorption per unit time of charged particles by measuring the voltage V _CGS of this time The amount, that is, the amount of charged particles can be detected.
[0024]
For example, to represent the relationship between the voltage V _CGS and the charge amount of particles is assumed on the basis of the output of the charged particle detection circuit in the graph is shown in Figure 3, based on the correlation between the voltage V _CGS charged particle amount, It is possible to detect the amount of charged particles based on the voltage V _CGS .
[0025]
As described above, the charged particle detection apparatus 1 shown in the present embodiment can detect the amount of charged particles by a small and lightweight field effect transistor type sensor structure. For this reason, it can be made small and light and can be easily incorporated into various devices.
[0026]
The charged particle detection apparatus 1 configured as in the present embodiment forms the insulating region after the source region 3 and the drain region 4 are formed on the silicon substrate 1 by ion implantation using a mask having a predetermined pattern. 5 is patterned, the floating gate 6 is mounted on the insulating film 5, and then the tunnel film 7 is formed, the control gate 8 is mounted, and the sidewall oxide film 9 is formed.
[Brief description of the drawings]
FIG. 1 is a diagram showing an overall configuration of a charged particle detection apparatus according to a first embodiment of the present invention.
FIG. 2 is a diagram showing an example of a charged particle detection circuit to which the charged particle detection device shown in FIG. 1 is applied.
FIG. 3 is a graph showing the relationship between voltage V _CGS and charged particle amount.
FIG. 4 is a diagram showing an overall configuration of a conventional charged particle detection apparatus.
[Explanation of symbols]
1 ... charged particle detector, 2 ... silicon substrate, 3 ... source region,
4 ... Drain region, 5 ... Insulating film, 6 ... Floating gate, 7 ... Tunnel film,
8 ... Control gate, 9 ... Side wall insulating film, 10 ... Low current circuit,
12: Low-pass filter.

Claims (3)

A semiconductor substrate (2);
A source region (3) and a drain region (4) formed so as to be separated from each other in a surface layer portion of the semiconductor substrate;
When a channel is formed between the source region and the drain region, a floating gate (6) formed with an exposed portion that is exposed to the outside air on the channel;
A control gate (8) for controlling the potential of the floating gate;
A charged particle detection apparatus comprising a tunnel film (7) disposed between the floating gate and the control gate. The floating gate, the control gate, and the tunnel film are formed on the channel via an insulating film (5), and the tunnel gate and the control gate are sequentially arranged with the floating gate being arranged in the center. The charged particle detection apparatus according to claim 1, wherein The potential of the control gate is adjusted so that the current (I _DS ) between the source region and the drain region is constant, and the concentration of charged particles is obtained based on the potential of the control gate. The charged particle detection apparatus according to claim 1 or 2, wherein

Images