Physics of Semiconductors: Applications of MIS Diodes in Flash Memory

This report explores the applications of MIS diodes in the electrical charging mechanism of Flash memory. It discusses the current-voltage and current-capacitance relations of MIS diodes and the working principle of Flash memory. It also examines the problems associated with current Flash technology and how nano-structures can eliminate these problems.

Physics of semiconductors
Student name1
Department, university
Address, containing the country name
1.0 Abstract-Diodes are used in various
applications due to their excellent features
and characteristics. Various types of diodes
are available for various applications. MIS
diodes for instance have been used in Flash
memory technology for efficient operations.
Despite of numerous problems facing the
current flash memory devices, the use of
nano-structures as storage elements have
been identified as potential for eliminating
the current problems and improving on the
efficiency of devices.
Keywords
Mis diode, flush memory, silicon
nanostructures
2.0 Introduction
Diodes are very significant in life as they
constitute the major components of logic
gates, transistor, amplifiers and integrated
circuits [2-4]. Depending on the desired
applications, there are several types of
diodes available. Metal insulator
semiconductor diode (MIS) is highly used in
the research and study of semiconductor
surfaces owing to their stability and
reliability. Presently, MIS diodes are used in
various electronics operations [7].
MISs can be further classified into different
categories like the metal oxide silicon.
Basically, MIS structure is viewed as a
voltage-capacitance related [4]. When
appropriate voltage is applied to the charge
coupled device, electrical charges are moved
across the entire semiconductor substrate in
a very controlled manner [8]. Therefore,
charge coupled devices have been used in a
variety of applications such as the logic
operations and signal processing. Figure 1
shows a schematic of a metal insulator
semiconductor diode.
Figure 1: Metal insulator semiconductor
diode
In this report, applications of an MIS diode
in the electrical charging mechanism of
Flash memory is investigated. It is based on
the description of the diode current-voltage
and current-capacitance relations.
Furthermore, the general working principle
of flash technology and associated problem
are presented.
3.0 Experimental Section
Requirements
 MIS diodes
 Flash memory device
 Connecting wires
 Power supply
 Digital multimeter
Procedure
1. The metal-insulator-semiconductor
(MIS) diodes were fabricated on
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silicon layer substrates. First, by a
diluted hydrogen fluoride (DHF) was
used to clean the silicon substrates.
Ultra-pure water (UPW) was then
used for rinsing operations for some
time to avoid surface roughness.
Finally, argon was used to pre-
sputter the hafnium target just before
film deposition.
2. Through the appropriate connection,
the electrical charging mechanism in
flash memory was examined and
analyzed.
3. Currents, voltages, capacitance and
time data were measure and recorded
in Microsoft Excel. Graphs for
current-voltage and capacitance
voltage were plotted and analyzed.
4. Discussions questions were finally
represented.
4.0 Results and discussion
From the recorded data, the following
graphs were plotted.
-40 -30 -20 -10 0 10 20 30 40
-0.000000001
-8E-10
-6E-10
-4E-10
-2E-10
0
2E-10
4E-10
6E-10
8E-10
0.000000001
Curent vs Voltage
Voltage (V)
Current (A)
Figure 2: Graph representing the Current vs
Voltage of the MIS diode
-40 -30 -20 -10 0 10 20
-2.00E-10
-1.00E-10
0.00E+00
1.00E-10
2.00E-10
3.00E-10
4.00E-10
Current vs Voltage
Voltage (V)
Current (A)
Figure 3: Graph representing the Current vs
Voltage of the MIS diode
-40 -30 -20 -10 0 10 20
1.39E-10
1.40E-10
1.41E-10
1.42E-10
1.43E-10
1.44E-10
1.45E-10
1.46E-10
Capacitance vs Voltage
Voltage (V)
Capacitance (F)
Figure 4: Graph representing the
Capacitance vs Voltage of the MIS diode
2

Q1. MIS Diode can be used to understand
the electrical charging mechanism in Flash
memory. Explain.
Generally, the electrical charging
mechanism of flash memories depends on
the floating gate transistors [1]. These
transistors help in adding and removing
electrons thus charging and discharging
respectively which enables data addition and
removal. The charging state of the floating
gate determines whether a bit is 0 or 1.
These floating gate transistors are made of
complementary metal-oxide semiconductor
which are a types of metal insulator
semiconductor diodes [5-6]. This is due to
their voltage and current properties in
various conditions.
Q2. Calculate the area enclosed by C-V
curves for memory device for C-V measured
at different frequencies. Is there any
difference among the enclosed areas of
memory device measured at different
frequencies? Explain the observation in your
own words.
For the curve in figure 2, the
enclosed are is given by
Area = 9.23454*10-5 μm2
There is a significant difference in
the enclosed areas of the memory
device at different frequency due to
the changing voltages and current
measurements. This also explains
changes in the charging and
discharge.
Q3. Use the CV data, to calculate the
charge storage in your memory devices.
Q = CV
= 2.5 *2* 10-11
= 5*10-10 C
Q4. Plot the retention data for “0” and “1”
states. What do you observe? Explain the
observation in your own words.
From the MIS diode and charge coupled
devices graph represented in figure 4, the
charge and discharge curves are used to
represent the 1 and 0 states respectively.
They are linear proportional to each other.
Q5. Explain the working principle of Flash
Memory and problems associated with
current Flash technology. Will the use of
nano-structures, as a storage element,
eliminate the problems associated with the
Flash memory? Justify your answer.
Flash memory comprises of memory cells
arranged in an array. Each and every cell has
one floating gate transistor for storage of at
least one bit. However, 1 information bit can
be stored using Single-Level Cells (SLCs
while more bits can be stored using Multi-
Level Cells (MLCs). This is enabled by
selecting between levels of electrical charge
in the floating gate transistor of a memory
cell [10].
Several problems are associated with current
flash memories. They include: poor data
infrastructure especially for large storages,
expensive cost, security and data corruption
[9].
Indeed, the use of nano-structures as storage
elements will eliminate the current
problems. For instance, they will reduce the
cost at large by reducing the size and
maximizing on the storage.
5.0 Conclusion
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In conclusion, MIS diodes are very essential
for several applications such as flash
memory devices. Despite of numerous
problems facing the current flash memory
devices, the use of nano-structures as
storage elements have been identified as
potential for eliminating the current
problems and improving on the efficiency of
devices.
Acknowledgements
I would like to thank my instructor and
fellow students for their continued support
during the laboratory practical and entire
course work.
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